Rohde&Schwarz FSW-K96 User Manual

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R&S®FSW-K96 OFDM Vector Signal Analysis Application User Manual

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1179384402 Version 02

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This manual applies to the following R&S®FSW models with firmware version 5.10 and later:

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R&S®FSW8 (1331.5003K08 / 1312.8000K08)

●

R&S®FSW13 (1331.5003K13 / 1312.8000K13)

●

R&S®FSW26 (1331.5003K26 / 1312.8000K26)

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R&S®FSW43 (1331.5003K43 / 1312.8000K43)

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R&S®FSW50 (1331.5003K50 / 1312.8000K50)

●

R&S®FSW67 (1331.5003K67 / 1312.8000K67)

●

R&S®FSW85 (1331.5003K85 / 1312.8000K85)

The following software options are described:

●

R&S®FSW-K96 (1313.1539.02)

© 2022 Rohde & Schwarz GmbH & Co. KG Muehldorfstr. 15, 81671 Muenchen, Germany Phone: +49 89 41 29 - 0 Email: info@rohde-schwarz.com Internet: www.rohde-schwarz.com Subject to change – data without tolerance limits is not binding. R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG. Trade names are trademarks of the owners.

1179.3844.02 | Version 02 | R&S®FSW-K96

Throughout this manual, products from Rohde & Schwarz are indicated without the ® symbol, e.g. R&S®FSW is indicated as R&S FSW.

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1 Welcome to the OFDM vector signal analysis (VSA) application......5

1.1 Introduction to vector signal analysis........................................................................ 5

1.2 Starting the R&S FSW OFDM VSA application...........................................................6

1.3 Understanding the display information...................................................................... 7

2 OFDM VSA measurement and results..................................................9

2.1 OFDM VSA parameters.................................................................................................9

2.2 Evaluation methods for OFDM VSA measurements................................................ 11

3 Measurement basics............................................................................29

3.1 OFDMA......................................................................................................................... 29

3.2 OFDM parameterization..............................................................................................30

Contents

3.3 Channel filter............................................................................................................... 36

3.4 OFDM measurement................................................................................................... 37

3.5 Sample rate and maximum usable I/Q bandwidth for RF input.............................. 40

3.6 OFDM VSA in MSRA operating mode....................................................................... 56

4 Configuring OFDM VSA measurements............................................ 58

4.1 Configuration overview.............................................................................................. 59

4.2 Signal description....................................................................................................... 60

4.3 Input, output and frontend settings...........................................................................64

4.4 Trigger settings........................................................................................................... 80

4.5 Data acquisition.......................................................................................................... 85

4.6 Sweep settings............................................................................................................ 89

4.7 Burst search................................................................................................................ 90

4.8 Result ranges.............................................................................................................. 91

4.9 Synchronization, demodulation and tracking.......................................................... 91

4.10 Adjusting settings automatically...............................................................................95

5 Creating a configuration file using the wizard.................................. 97

5.1 Understanding the R&S FSW-K96 Configuration File Wizard display................... 97

5.2 Configuration steps.................................................................................................. 105

5.3 Reference of wizard menu functions.......................................................................112

5.4 Example: creating a configuration file from an input signal.................................115

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6 Analyzing OFDM VSA vector signals............................................... 123

6.1 Result configuration................................................................................................. 123

6.2 Table configuration................................................................................................... 125

6.3 Units........................................................................................................................... 126

6.4 Y-scaling.................................................................................................................... 126

6.5 Markers...................................................................................................................... 128

6.6 Trace / data export configuration............................................................................ 134

6.7 Analysis in MSRA mode........................................................................................... 136

7 How to perform measurements in the R&S FSW OFDM VSA appli-

8 Remote commands for the R&S FSW OFDM VSA application...... 140

8.1 Introduction............................................................................................................... 140

Contents

cation...................................................................................................138

8.2 Common suffixes...................................................................................................... 145

8.3 Activating the R&S FSW OFDM VSA application...................................................146

8.4 Configuring the R&S FSW OFDM VSA application................................................149

8.5 Performing a measurement......................................................................................238

8.6 Analysis..................................................................................................................... 243

8.7 Configuring the result display................................................................................. 267

8.8 Retrieving results......................................................................................................276

8.9 Status reporting system........................................................................................... 301

8.10 Deprecated commands.............................................................................................304

8.11 Programming examples: OFDM vector signal analysis........................................ 305

Annex.................................................................................................. 309

A Formulae.............................................................................................309

A.1 Error vector magnitude (EVM)................................................................................. 309

A.2 I/Q impairments......................................................................................................... 310

B Reference: IQW format specification for user-defined constellation

points...................................................................................................311

List of commands (OFDM VSA)........................................................ 313

Index....................................................................................................321

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1 Welcome to the OFDM vector signal analy-

Welcome to the OFDM vector signal analysis (VSA) application

Introduction to vector signal analysis

sis (VSA) application

The R&S FSW OFDM VSA application performs vector and scalar measurements on digitally modulated OFDM signals. To perform the measurements it converts RF signals into the complex baseband.

The R&S FSW OFDM VSA application features:

●

Analysis of non-standard and standard-conform OFDM systems

●

I/Q-based measurement results such as EVM, constellation diagrams, power spectrum

This user manual contains a description of the functionality that the application provides, including remote control operation.

Functions that are not discussed in this manual are the same as in the Spectrum application and are described in the R&S FSW base unit user manual.

The latest version is available for download at the product homepage http://

www.rohde-schwarz.com/product/FSW.

● Introduction to vector signal analysis........................................................................ 5

● Starting the R&S FSW OFDM VSA application........................................................ 6

● Understanding the display information......................................................................7

1.1 Introduction to vector signal analysis

The goal of vector signal analysis is to determine the quality of the signal that is transmitted by the device under test (DUT) by comparing it against an ideal signal. The DUT is usually connected with the analyzer via a cable. The key task of the analyzer is to determine the ideal signal. Hence, the analyzer aims to reconstruct the ideal signal from the measured signal that is transmitted by the DUT. This ideal signal is commonly referred to as the reference signal, while the signal from the DUT is called the mea- surement signal.

After extracting the reference signal, the R&S FSW OFDM VSA application compares the measurement signal and the reference signal, and the results of this comparison are displayed.

Example:

The most common vector signal analysis measurement is the EVM ("Error Vector Magnitude") measurement. Here, the complex baseband reference signal is subtracted from the complex baseband measurement signal. The magnitude of this error vector represents the EVM value. The EVM has the advantage that it "summarizes" all potential errors and distortions in one single value. If the EVM value is low, the signal quality of the DUT is high.

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1.2 Starting the R&S FSW OFDM VSA application

Welcome to the OFDM vector signal analysis (VSA) application

Starting the R&S FSW OFDM VSA application

Figure 1-1: Simplified schema of vector signal analysis

The R&S FSW OFDM VSA application adds a new application to the R&S FSW.

To activate the R&S FSW OFDM VSA application

1. Select the [MODE] key. A dialog box opens that contains all operating modes and applications currently

available on your R&S FSW.

2. Select the "OFDM VSA" item.

The R&S FSW opens a new measurement channel for the R&S FSW OFDM VSA application.

Multiple Measurement Channels and Sequencer Function

When you activate an application, a new measurement channel is created which determines the measurement settings for that application. The same application can be activated with different measurement settings by creating several channels for the same application.

The number of channels that can be configured at the same time depends on the available memory on the instrument.

Only one measurement can be performed at any time, namely the one in the currently active channel. However, in order to perform the configured measurements consecutively, a Sequencer function is provided.

If activated, the measurements configured in the currently active channels are performed one after the other in the order of the tabs. The currently active measurement is indicated by a

symbol in the tab label. The result displays of the individual channels

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1.3 Understanding the display information

Welcome to the OFDM vector signal analysis (VSA) application

Understanding the display information

are updated in the tabs (as well as the "MultiView") as the measurements are performed. Sequential operation itself is independent of the currently displayed tab.

For details on the Sequencer function see the R&S FSW User Manual.

The following figure shows a measurement diagram during analyzer operation. All different information areas are labeled. They are explained in more detail in the following sections.

= Channel bar for firmware and measurement settings

2+3 = Window title bar with diagram-specific (trace) information 4 = Diagram area 5 = Diagram footer with diagram-specific information, depending on measurement application 6 = Instrument status bar with error messages, progress bar and date/time display

Channel bar information

In the R&S FSW OFDM VSA application, the R&S FSW shows the following settings:

Table 1-1: Information displayed in the channel bar in R&S FSW OFDM VSA application

Label Description

Ref Level Reference level

Att Mechanical and electronic RF attenuation

Input Input type of the signal source

Offset Reference level offset

Freq Center frequency for the RF signal

Capture Time How long data was captured in current sweep

Sample Rate Sample rate

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Welcome to the OFDM vector signal analysis (VSA) application

Understanding the display information

Label Description

FFT FFT size

CP Length Cyclic prefix length

Res Len Result length

Config Currently loaded configuration file

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 FSW base unit user manual.

Window title bar information

For each diagram, the header provides the following information:

Figure 1-2: Window title bar information in R&S FSW OFDM VSA application

1 = Window name 2 = Result type 3 = Trace color 4 = Trace number 5 = Trace mode

Diagram area

The diagram area displays the results according to the selected result displays (see

Chapter 2.2, "Evaluation methods for OFDM VSA measurements", on page 11).

Diagram footer information

The diagram footer (beneath the diagram) contains the start and stop symbols or time of the evaluation range.

Status bar information

The software status, errors and warnings and any irregularities in the software are indicated in the status bar at the bottom of the R&S FSW window.

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2 OFDM VSA measurement and results

2.1 OFDM VSA parameters

OFDM VSA measurement and results

OFDM VSA parameters

Access: "Overview" > "Display Config"

Or: [MEAS] > "Display Config"

The R&S FSW OFDM VSA application provides various different result displays for OFDM VSA measurements.

● OFDM VSA parameters............................................................................................ 9

● Evaluation methods for OFDM VSA measurements...............................................11

Several signal parameters are determined during vector signal analysis and displayed in the Result Summary.

For details concerning the calculation of individual parameters, see Chapter A, "Formu-

lae", on page 309.

Evaluated cells for EVM and MER results

For the numerical EVM and MER results described in Table 2-1, only the symbols in the specified result length are evaluated. The following cells and carriers are ignored:

●

All "don't care" cells in all carriers

●

All zero cells in all carriers

●

All guard carriers, which consist of zero cells or "don't care" cells only

●

DC carriers, which consist of zero cells only

Note that for the "EVM vs Carrier", "EVM vs Symbol" and "EVM vs Symbol vs Carrier" results, the traces include the zero cells and DC carriers to avoid gaps.

Table 2-1: OFDM VSA parameters

Parameter Description SCPI parameter *)

EVM All [%/dB] Error Vector Magnitude of all pilot and data cells of the ana-

lyzed frames

EVM Data Symbols [%/dB]

EVM Pilot Symbols [%/dB]

**) Maximum EVM of each carrier (frequency domain) and in

Error Vector Magnitude of all data cells of the analyzed frames. All pilot cells are ignored.

Error Vector Magnitude of all pilot cells of the analyzed frames. All data cells are ignored.

each symbol (time domain) for each analyzed signal frame. The results are provided in dB or percent.

Corresponds to the maximum of the peaks for each frame in the EVM vs Symbol vs Carrier display.

EVM[:ALL]

EVM:DATA

EVM:PILot

EVMPeak[:ALL]

*) Required to retrieve the parameter result, see Chapter 8.8.1, "Retrieving numerical results", on page 276 **) not included in Result Summary, remote query only

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OFDM VSA measurement and results

OFDM VSA parameters

Parameter Description SCPI parameter *)

**) Maximum EVM of each carrier (frequency domain) and in

each data symbol (time domain) for each analyzed signal frame. The results are provided in dB or percent.

**) Maximum EVM of each carrier (frequency domain) and in

each pilot symbol (time domain) for each analyzed signal frame. The results are provided in dB or percent.

MER [dB] Average Modulation Error Ratio (MER) for all data and all

pilot cells of the analyzed frames. If more than one frame is evaluated, mean square averaging is used.

The MER is the ratio of the RMS power of the ideal reference signal to the RMS power of the error vector.

For the average MER, the ratio of (power of the error vector) to (power of the ideal reference signal) is averaged.

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 sig-

nal relative to the amplification of the in-phase component

Quadrature error [°] Phase angle between Q-channel and I-channel deviating

from the ideal 90 degrees; measure for crosstalk from the Qbranch into the I-branch

Frequency Error [Hz] Frequency error between the signal and the currently defined

center frequency The absolute frequency error includes the frequency error of

the R&S FSW and that of the DUT. If possible, the transmitter R&S FSW and the DUT should be synchronized (using an external reference).

EVMPeak:DATA

EVMPeak:PILot

MER[:ALL]

IQOFset

GIMBalance

QUADerror

FERRor

Sample Clock Error Clock error between the signal and the sample clock of the

R&S FSW in parts per million (ppm), i.e. the symbol timing error

If possible, the transmitter R&S FSW and the DUT should be synchronized (using an external reference).

Frame Power Average time domain power of the analyzed signal frame

Crest factor [dB] The ratio of the peak power to the mean power of the ana-

lyzed signal frame

*) Required to retrieve the parameter result, see Chapter 8.8.1, "Retrieving numerical results", on page 276 **) not included in Result Summary, remote query only

SERRor

POWer

CRESt

The R&S FSW OFDM VSA application also performs statistical evaluation over several frames and displays the following results:

Table 2-2: Calculated summary results

Result type Description

Min Minimum measured value

Average Average measured value

Max Maximum measured value

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2.2 Evaluation methods for OFDM VSA measurements

OFDM VSA measurement and results

Evaluation methods for OFDM VSA measurements

The data that was measured by the R&S FSW can be evaluated using various different methods without having to start a new measurement. Which results are displayed depends on the selected evaluation.

The R&S FSW OFDM VSA application provides the following evaluation methods:

Allocation Matrix............................................................................................................ 11

Bitstream.......................................................................................................................12

CCDF............................................................................................................................ 14

Channel Flatness.......................................................................................................... 14

Constellation Diagram...................................................................................................15

Constellation vs Carrier.................................................................................................16

Constellation vs Symbol................................................................................................17

EVM vs Carrier..............................................................................................................18

Constellation vs Symbol................................................................................................18

EVM vs Symbol vs Carrier............................................................................................ 19

Group Delay..................................................................................................................20

Impulse Response........................................................................................................ 20

Magnitude Capture........................................................................................................21

Marker Table................................................................................................................. 22

Notes.............................................................................................................................22

Power Spectrum............................................................................................................22

Power vs Carrier........................................................................................................... 23

Power vs Symbol.......................................................................................................... 24

Power vs Symbol vs Carrier..........................................................................................25

Result Summary............................................................................................................26

Signal Flow....................................................................................................................27

Trigger to Sync..............................................................................................................27

Allocation Matrix

The Allocation Matrix display is a graphical representation of the OFDM cell structure defined in the currently loaded configuration file.

Use markers to get more detailed information on the individual cells.

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OFDM VSA measurement and results

Evaluation methods for OFDM VSA measurements

Figure 2-1: Allocation Matrix

The legend for the color coding is displayed at the top of the matrix. Note: Markers in the Allocation Matrix. Using markers you can detect individual alloca-

tion points for a specific symbol or carrier. When you activate a marker in the Allocation Matrix, its position is defined by the symbol and carrier number the point belongs to. The marker result indicates the I and Q values of the point. See also "Markers in the Constellation View and Allocation Matrix" on page 129.

Remote command:

LAY:ADD? '1',RIGH,AMATrix, see LAYout:ADD[:WINDow]? on page 269

TRACe<n>[:DATA]? on page 290, see Chapter 8.8.4.1, "Allocation matrix",

on page 294

TRACe<n>[:DATA]:X? on page 290 TRACe<n>[:DATA]:Y? on page 291

Symbol unit: UNIT:SAXes on page 250

Bitstream

This result display shows a demodulated data stream for the symbols in the currently analyzed result ranges. The different modulation types are indicated by color, as shown in the legend at the top of the window. Guard carriers are not included in the display, but are returned as non-data cells ("---") in trace export files.

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OFDM VSA measurement and results

Evaluation methods for OFDM VSA measurements

The bitstream is derived from the order of the constellation points in the configuration file.

Example:

For QPSK, the value that is in the first position defines "00", the value that is in the second position defines "01", the value that is in the third position "10" and the last value "11".

Figure 2-2: Extract from configuration file defining the constellation points

Remote command:

LAY:ADD? '1',RIGH,BITS, see LAYout:ADD[:WINDow]? on page 269 TRACe:DATA?, see Chapter 8.8.4.2, "Bitstream", on page 295

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OFDM VSA measurement and results

Evaluation methods for OFDM VSA measurements

CCDF

The CCDF results display shows the probability of an amplitude exceeding the mean power. The x-axis displays power relative to the measured mean power.

Figure 2-3: CCDF display

Remote command:

LAY:ADD? '1',RIGH,CCDF, see LAYout:ADD[:WINDow]? on page 269 TRACe:DATA?, see Chapter 8.8.4.3, "CCDF", on page 295

TRACe<n>[:DATA]:X? on page 290

Channel Flatness

The Channel Flatness display shows the amplitude of the channel transfer function vs. carrier.

The statistic is performed over all analyzed frames.

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OFDM VSA measurement and results

Evaluation methods for OFDM VSA measurements

Figure 2-4: Channel Flatness Display

Remote command:

LAY:ADD? '1',RIGH,CHFL, see LAYout:ADD[:WINDow]? on page 269 TRACe:DATA?, see Chapter 8.8.4.4, "Channel flatness", on page 295

TRACe<n>[:DATA]:X? on page 290

Carrier unit: UNIT:CAXes on page 249

Constellation Diagram

The Constellation Diagram shows the inphase and quadrature results for the analyzed input data. The ideal points for the selected cell types are displayed for reference purposes.

Figure 2-5: Constellation diagram

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OFDM VSA measurement and results

Evaluation methods for OFDM VSA measurements

The legend for the color coding is displayed at the top of the matrix. If you click on one of the codes, only the selected constellation points are displayed. Click again, and all constellation points are displayed again (according to the constellation filter).

See Chapter 6.1, "Result configuration", on page 123. Note: Markers in the Constellation diagram. Using markers you can detect individual

constellation points for a specific symbol or carrier. When you activate a marker in the Constellation diagram, its position is defined by the symbol and carrier number the point belongs to. The marker result indicates the I and Q values of the point.

Figure 2-6: Marker in a Constellation diagram

3 Measurement basics

3.1 OFDMA

Measurement basics

OFDMA

Some background knowledge on basic terms and principles used in OFDM vector signal analysis is provided here for a better understanding of the required configuration settings.

● OFDMA................................................................................................................... 29

● OFDM parameterization..........................................................................................30

● Channel filter...........................................................................................................36

● OFDM measurement...............................................................................................37

● Sample rate and maximum usable I/Q bandwidth for RF input...............................40

● OFDM VSA in MSRA operating mode.................................................................... 56

In an OFDM system, the available spectrum is divided into multiple carriers, called subcarriers, which are orthogonal to each other. Each of these subcarriers is independently modulated by a low rate data stream.

OFDM is used as well in WLAN, WiMAX and broadcast technologies like DVB. OFDM has several benefits including its robustness against multipath fading and its efficient receiver architecture.

Figure 3-1 shows a representation of an OFDM signal taken from 3GPP TR 25.892.

Data symbols are independently modulated and transmitted over a high number of closely spaced orthogonal subcarriers. In the OFDM-VSA common modulation schemes as QPSK, 16QAM, and 64QAM can be defined as well as arbitrarily distributed constellation points.

In the time domain, a guard interval can be added to each symbol to combat interOFDM-symbol-interference due to channel delay spread. In EUTRA, the guard interval is a cyclic prefix which is inserted before each OFDM symbol.

Figure 3-1: Frequency-time representation of an OFDM signal

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Measurement basics

OFDM parameterization

In practice, the OFDM signal can be generated using the inverse fast Fourier transform (IFFT) digital signal processing. The IFFT converts a number N of complex data symbols used as frequency domain bins into the time domain signal. Such an N-point IFFT is illustrated in Figure 3-2, where a(mN+n) refers to the nth subchannel modulated data symbol, during the time period mTu < t ≤ (m+1)Tu.

Figure 3-2: OFDM useful symbol generation using an IFFT

The vector sm is defined as the useful OFDM symbol. It is the time superposition of the N narrowband modulated subcarriers. Therefore, from a parallel stream of N sources

of data, each one independently modulated, a waveform composed of N orthogonal subcarriers is obtained. Each subcarrier has the shape of a frequency sinc function (see Figure 3-1).

Figure 3-3 illustrates the mapping from a serial stream of QAM symbols to N parallel

streams, used as frequency domain bins for the IFFT. The N-point time domain blocks obtained from the IFFT are then serialized to create a time domain signal. Not shown in Figure 3-3 is the process of cyclic prefix insertion.

Figure 3-3: OFDM signal generation chain

3.2 OFDM parameterization

A generic OFDM analyzer supports various OFDM standards. Therefore a common parameterization of OFDM systems has to be defined.

● Time domain description.........................................................................................30

● Frequency domain description................................................................................31

● Preamble description.............................................................................................. 35

3.2.1 Time domain description

The fundamental unit of an OFDM signal in the time domain is a sample.

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An OFDM symbol with a length of NS samples consists of:

●

A guard interval of length N

●

An FFT interval of length N

FFT

Measurement basics

OFDM parameterization

Figure 3-4: OFDM symbol in time domain

3.2.2 Frequency domain description

The FFT intervals of the OFDM symbols are transformed into the frequency domain using a discrete Fourier transformation. The successive symbols of the OFDM signal are displayed in time-frequency matrices. The fundamental unit of an OFDM signal in the frequency domain is a cell.

The total area of a time-frequency matrix is called frame. A frame is the highest level unit used in OFDM VSA.

FFT

Figure 3-5: Time-Frequency matrix

Carriers

A column of cells at the same frequency is called carrier.

The carrier number is the column index of a time-frequency matrix. The number '0' is assigned to the DC-carrier, which lies at the transmitter center frequency. The total

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FFT

 



 



 1

FFTFFT

FFT

N 

 



 







FFTFFT

Measurement basics

OFDM parameterization

number of subcarriers is N carrier relative to the lowermost subcarrier. The offset is an inherent attribute of the

FFT algorithm.

Table 3-1: Relationship between FFT length and subcarrier range

FFT length N

even

odd

OFDM system sample rate

In an OFDM system, an FFT (with the length N FFT bin corresponds to one subcarrier. For each FFT bin, one sample must be cap-

tured in the time domain for each OFDM symbol. The minimum number of samples required for the measurement is thus the number of subcarriers (or the number of FFT bins), multiplied by the number of symbols to measure. To avoid intersymbol interference, the cyclic prefix is added as the guard interval.

No_samples

FFT

= (<FFT_size> + <CyclicPrefixLength>) * <No_symbols_to_measure>

min

. The DC-carrier offset determines the position of the DC

FFT

DC-Carrier offset Range

) is performed for each symbol. Each

FFT

Generally, the number of samples acquired per second is referred to as the sample rate. The sample rate required by a specific OFDM system is referred to as the OFDM system sample rate. It depends on parameters that characterize the OFDM system and is defined by the following equation:

For the R&S FSW OFDM VSA application to demodulate OFDM symbols, it is important that the number of acquired samples in the application corresponds to the OFDM system sample rate.

Symbols

A row of cells at the same time is called symbol.

The symbol number is the row index of a time frequency matrix. The first symbol gets the number '0'.

3.2.2.1 Allocation matrix

The allocation matrix defines the complete frame and subdivides the OFDM system into the following cell types:

●

= <carrier_spacing>* <FFT_size>

OFDM

Pilot cells: Contain known values and are used for various synchronization and parameter estimation purposes.

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Measurement basics

OFDM parameterization

●

Data cells: Contain the user data or payload of the transmission. The modulation format of the data cells must be known or can be estimated in a modulation estimation block.

●

"Don't Care" cells: Cells that are not evaluated for EVM measurement, but contain signal power.

●

Zero cells: Contain no signal power at all; Typically, guard carriers around DC or at the edges of the carrier axis.

Figure 3-6: Allocation matrix

3.2.2.2 Pilot matrix

A pilot matrix contains known complex numbers in the matrix cells, which are defined as pilot cells in the allocation matrix. Within the analyzer, the pilot matrix is correlated with the received time frequency matrix. Thus, it obtains the frame start and the frequency offset of the received signal relative to the given allocation matrix.

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





Measurement basics

OFDM parameterization

Figure 3-7: Pilot matrix

3.2.2.3 Constellation vector

A constellation vector contains all possible numbers in the complex plane that belong to a specific modulation format. Constellation vectors must be defined for each possible data modulation format. The magnitude within the constellation vectors must be scaled according to the pilot matrix. One entry in the constellation vector is called con- stellation point'.

Differential modulation is not supported. The respective absolute modulation scheme must be used instead (e.g. QPSK instead of DQPSK). Periodically rotated constellations are not supported. The set union of all constellations must be used instead (e.g. 8PSK instead of PI/4-DQPSK).

Figure 3-8: QPSK constellation vector

Constellation point

3.2.2.4 Modulation matrix

A modulation matrix contains numbers to the underlying constellation vector for each cell, which is defined as data cell in the allocation matrix. Clusters of data cells with the same modulation therefore share the same number. A data cell can also contain an unused number, that is a number for which no constellation vector is defined. In this

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Measurement basics

OFDM parameterization

case, all data cells sharing that number are assumed to use only one of the valid constellation vectors. This method can be used within the R&S FSW OFDM VSA application to allow for automatic modulation detection.

Figure 3-9: Modulation matrix

3.2.3 Preamble description

The OFDM demodulator must support synchronization on repetitive preamble symbols. A repetitive preamble contains several repetitions of one time domain block. The Fig-

ure 3-10 shows exemplarily the parameterization of a repetitive preamble symbol,

which contains a five times repetition of block T. The allocation matrix can have an arbitrary offset to the beginning of the preamble symbol. If the offset is zero or negative, the preamble is also contained within the frame and is used for further estimation processes.

Preamble Symbol

Figure 3-10: Description of a repetitive preamble symbol

T3 T4 T5

Frame Offset

Block length

Undefined

Symbol 0

Frame (Structure Matrix)

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0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Normalized Frequency

Frequency Response [dB]

Adjustable Channel Filter

Low Normal High

3.3 Channel filter

Measurement basics

Channel filter

The R&S FSW OFDM VSA application can use the internal channel filter of the instrument or apply an adjustable channel filter. The filter bandwidth of the internal channel filter is fully equalized within the digital hardware.

Alternatively to the internal filters, you can apply a channel filter with adjustable bandwidth and slope characteristics to the input signal. The R&S FSW OFDM VSA application then designs a window-based finite impulse response filter. The bandwidth is defined as two times the 6-dB cutoff frequency. The 50-dB cutoff frequency determines the slope characteristics.

Choosing the correct filter settings is a trade-off between selectivity and filter impulse response length. A steep filter leads to superior selectivity between adjacent channels. On the other hand, such a filter has a long channel impulse response, which can produce intersymbol interference if used in systems with small guard intervals. Flat filters require a higher distance between channels and possibly attenuate the outer carriers of the signal. In contrast, the channel impulse response is short and suited for systems with short guard intervals.

Figure 3-11: Slope characteristics for different channel filters (with low, normal, high steepness)

The adjustable channel filter performs a decimation at its output. Thus, the user-definable maximum output sample rate is reduced compared to the internal filter setting. Therefore, data is captured by the R&S FSW with an oversampling factor before the adjustable channel filter is applied.

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OFDM measurement

Example:

Assume you want to analyze a 20-MHz WLAN-A signal. The specified (demodulation) sample rate is 20 MHz.

If the adjustable channel filter is disabled, the R&S FSW captures I/Q data and resamples it to 20 MHz. The instrument's hardware defines the flat bandwidth, filter slope and stopband frequency of the used filter. The R&S FSW OFDM VSA application receives the data with the required sample rate of 20 MHz.

If the adjustable channel filter is enabled, the R&S FSW captures I/Q data using a doubled sample rate of 40 MHz, that is: an oversampling factor of 2 is applied. The R&S FSW OFDM VSA application then applies the adjustable channel filter. The userdefined 6-dB bandwidth defines the overall bandwidth of the filter. The distance between the 6-dB bandwidth and the user-defined 50-dB bandwidth defines the filter slope (see Figure 3-11). The 20-MHz region of interest in the middle of the signal is not affected by the filter. Finally, the R&S FSW OFDM VSA application decimates the filtered data from 40 MHz to the required sample rate of 20 MHz.

3.4 OFDM measurement

ON / OFF

Capture

Buffer

R_lk

A_lk

Burst

Detection

Freq / Clock

Estimation

A_lk A_lk

Freq / Clock

Estimation

Figure 3-12: Block diagram of the R&S FSW OFDM VSA application

PREAMBLE / CP

Time Sync

Compensate

Freq. / Clock Offset Channel CPE / Gain

Compensate

Freq. / Clock Offset Channel CPE / Gain

Compensate

Freq. Offset

Estimation

Rough

Channel

User Defined Compensation

FFT_SHIFT

FFT

CPE / Gain

Estimation

Data Aided Block Measurement Block

CPE / Gain

Estimation

EVM Measurement

R_lk w/o frame sync

Compensate

Modulation

Detection

MAX_BIN_OFFSET

Frame

Sync

Synchronization Block

Data

Decision

PHASE_TRACKING TIMING_TRACKING

GAIN_TRACKING CHANNEL_COMP

Pilot Aided Block

R_lk

A_lkR_lk

The block diagram in Figure 3-12 shows the R&S FSW OFDM VSA application process from the capture buffer containing the I/Q data to the actual analysis block. The signal processing chain can be divided in four major blocks:

● Synchronization block............................................................................................. 38

● Pilot-aided block......................................................................................................38

● Data aided block..................................................................................................... 39

● Measurement block.................................................................................................39

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3.4.1 Synchronization block

Measurement basics

OFDM measurement

The synchronization starts with a burst detection that extracts transmission areas within a burst signal by a power threshold. For seamless transmission, as is the case in most broadcast systems, it is possible to bypass this block. The following time synchronization uses either the preamble or the cyclic prefix of each OFDM symbol to find the optimum starting point for the FFT by a correlation metric. If preamble synchronization is selected, the correlation is done between successive blocks of a repetitive preamble structure. Alternatively, the cyclic prefix synchronization correlates the guard interval of each symbol with the end of the FFT part. In addition, both methods return an estimation of the fractional frequency offset by evaluating the phase of the correlation maximum. This frequency offset has to be compensated before the FFT to avoid intercarrier interference.

By default, the FFT starting point is put in the center of the guard interval assuming a symmetric impulse response, but it can optionally be shifted within the guard interval. After performing the FFT for each available OFDM symbol, a time-frequency matrix R

with symbol index l and subcarrier index k is available.

The subsequent frame synchronization determines the frame start within this matrix and the integer carrier frequency offset. It is determined by a two-dimensional correlation of R

with the known pilot matrix from the configuration file. To avoid unnecessary

l,k

computing time for signals with low frequency offset, the search length in the frequency direction can be limited by a control parameter.

l,k

Furthermore, a threshold for the reliability of time and frame synchronization can be defined to ensure that only correct frames are evaluated. A threshold is particularly useful for 5G signals, for example. In this case, the pilot structure in the second half of the frame is similar, but not identical to the first half. Thus, frame synchronization can be off by half a frame, but since the pilots do not match completely, the reliability is poor. The EVM results are also poor. By defining a threshold, only the correctly synchronized frames are evaluated.

3.4.2 Pilot-aided block

The pilot-aided block within the signal processing chain uses the predefined pilot cells for parameter estimation and subsequent compensation of the signal impairments. It starts with maximum likelihood estimation of the remaining frequency error and sample clock offset. While a frequency error leads to a phase offset linearly increasing with time, the clock offset introduces an additional phase error linearly increasing with frequency. The estimator determines the most probable parameters that lead to the phase offsets observed on the pilot cells. The resulting offset values are compensated in the frequency domain by rerotating the phase of the R

clock offsets it can be necessary to resample the received signal in the time domain and repeat the FFT stage.

The subsequent channel estimator determines the channel transfer function at the known pilot positions and uses interpolation to get a complete frequency response vector for all subcarriers. It does not extrapolate the channel transfer function for the guard carriers (which are defined by zero or "don't care" cell types). Since the presented measurement system is intended for stationary channels, the interpolation is performed

matrix. However, for severe

l,k

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OFDM measurement

along the frequency direction only. The node values on the frequency axis are determined by averaging all available pilots of each subcarrier over time. Depending on the layout of the pilots on the frequency axis, an interpolation filter bank with optimum Wiener filter coefficients is calculated in advance. The Wiener filter is designed under the assumption that the maximum impulse response length does not exceed the cyclic prefix length.

Although the channel is assumed to be stationary, common phase error and power level variations are estimated symbol by symbol over the complete frame. The estimation takes settling effects of oscillators and power amplifiers into account. All estimated impairments are fully compensated to get an optimum signal for the subsequent modulation-detection and data decision stage.

The modulation-detection block determines the modulation type of the data cells. Either each carrier or each symbol can be assigned to one specific constellation. Alternatively, the modulation information provided in the configuration file is evaluated to extract clusters of data cells with consistent modulation. The estimator uses a maximum likelihood approach. Each cluster of data cells is compared with all possible modulation hypotheses and the most probable constellation for each cluster is used for the subsequent data decision. The data decision block finally outputs a reference signal matrix A

which is an optimum estimate of the actual transmitted OFDM frame.

l,k

3.4.3 Data aided block

The data aided block can be activated optionally to refine the parameter estimations with the help of the reference signal. Whereas the previous stages could only include pilot cells for the estimation algorithms, the data aided part can treat data cells as additional pilots. Thus, the accuracy of the estimates increases in good signal to noise environments without data decision errors. However, if the reference signal matrix A

contains falsely decided data cells, the data aided estimation part can corrupt the results and should be omitted.

3.4.4 Measurement block

The last part of the signal processing chain comprises the user-defined compensation and the measurement of modulation quality. The measurement block takes the received OFDM symbols R

to calculate the error vector magnitude (EVM). The received OFDM symbols can

l,k

optionally be compensated using phase, timing and level deviations and the channel transfer function.

and the previously determined reference OFDM symbols

l,k

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3.5 Sample rate and maximum usable I/Q bandwidth for

Measurement basics

Sample rate and maximum usable I/Q bandwidth for RF input

RF input

Definitions

●

Input sample rate (ISR): the sample rate of the useful data provided by the device connected to the input of the R&S FSW

●

(User, Output) Sample rate (SR): the user-defined sample rate (e.g. in the "Data Acquisition" dialog box in the "I/Q Analyzer" application) which is used as the basis for analysis or output

●

Usable I/Q (analysis) bandwidth: the bandwidth range in which the signal remains undistorted in regard to amplitude characteristic and group delay; this range can be used for accurate analysis by the R&S FSW

●

Record length: the number of I/Q samples to capture during the specified measurement time; calculated as the measurement time multiplied by the sample rate

For the I/Q data acquisition, digital decimation filters are used internally in the R&S FSW. The passband of these digital filters determines the maximum usable I/Q bandwidth. In consequence, signals within the usable I/Q bandwidth (passband) remain unchanged, while signals outside the usable I/Q bandwidth (passband) are suppressed. Usually, the suppressed signals are noise, artifacts, and the second IF sideband. If frequencies of interest to you are also suppressed, try to increase the output sample rate, which increases the maximum usable I/Q bandwidth.

Bandwidth extension options

You can extend the maximum usable I/Q bandwidth provided by the R&S FSW in the basic installation by adding options. These options can either be included in the initial installation (B-options) or updated later (U-options). The maximum bandwidth provided by the individual option is indicated by its number, for example, B40 extends the bandwidth to 40 MHz.

Note that the U-options as of U40 always require all lower-bandwidth options as a prerequisite, while the B-options already include them.

As a rule, the usable I/Q bandwidth is proportional to the output sample rate. Yet, when the I/Q bandwidth reaches the bandwidth of the analog IF filter (at very high output sample rates), the curve breaks.

● Available bandwidth extension options................................................................... 41

● Relationship between sample rate, record length and usable I/Q bandwidth......... 41

● R&S FSW without additional bandwidth extension options.................................... 44

● R&S FSW with I/Q bandwidth extension option B40 or U40...................................44

● R&S FSW with I/Q bandwidth extension option B80 or U80...................................45

● R&S FSW with activated I/Q bandwidth extension option B160 or U160............... 45

● R&S FSW with activated I/Q bandwidth extension option B320/U320................... 46

● R&S FSW with activated I/Q bandwidth extension option B512............................. 47

● R&S FSW with activated I/Q bandwidth extension option B1200........................... 48

● R&S FSW with activated I/Q bandwidth extension option B2001........................... 50

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3.5.1 Available bandwidth extension options

Measurement basics

Sample rate and maximum usable I/Q bandwidth for RF input

● R&S FSW with activated I/Q bandwidth extension option B2000........................... 52

● R&S FSW with activated I/Q bandwidth extension option B5000........................... 53

● R&S FSW with activated I/Q bandwidth extension option B4001/B6001/B8001.... 54

Table 3-2: Available bandwidth extension options

Max. usable I/Q bandwidth

28 MHz - -

40 MHz B40 U40

80 MHz B80 U40+U80 or

160 MHz B160 U40+U80+U160 or

320 MHz B320 U40+U80+U160+U320 or

512 MHz B512 U40+U80+U512 or

1200 MHz B1200 B40 + U80 + U1200 or

Required B-option Required U-options

B40+U80

B40+U80+U160 or B80+U160

B40+U80+U160+U320 or B80+U160+U320 or B160+U320

B40+U80+U512 or B80+U512 or

B80 + U1200

2000 MHz B2000 U2000

2000 MHz B2001 U2001

4000 MHz B4001 U4001

5000 MHz B5000 U5000

6000 MHz B6001 U6001

8000 MHz B8001 U8001

3.5.2 Relationship between sample rate, record length and usable I/Q bandwidth

Up to the maximum bandwidth, the following rule applies:

Usable I/Q bandwidth = 0.8 * Output sample rate

Regarding the record length, the following rule applies:

Record length = Measurement time * sample rate

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Maximum record length for RF input

The maximum record length, that is, the maximum number of samples that can be captured, depends on the sample rate.

For activated option B1200, see Table 3-14.

For activated option B2001, see Chapter 3.5.10, "R&S FSW with activated I/Q band-

width extension option B2001", on page 50.

For activated option B2000, see Chapter 3.5.11, "R&S FSW with activated I/Q band-

width extension option B2000", on page 52.

For activated option B5000, see Chapter 3.5.12, "R&S FSW with activated I/Q band-

width extension option B5000", on page 53.

For activated option B4001/B6001/B8001, see Chapter 3.5.13, "R&S FSW with activa-

ted I/Q bandwidth extension option B4001/B6001/B8001", on page 54.

Table 3-3: Maximum record length (without I/Q bandwidth extension options R&S FSW-B160/-B320/-

Sample rate Maximum record length

100 Hz to 200 MHz 440 Msamples

200 MHz to 20 GHz (upsampling)

B512/-B1200/-B2001/-B4001/-B6001/-B8001)

220 Msamples

The Figure 3-13 shows the maximum usable I/Q bandwidths depending on the output sample rates.

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Usable I/Q bandwidth [MHz]

160

150

140

130

120

110

100

Sample rate and maximum usable I/Q bandwidth for RF input

I/Q bandwidths for RF input

Wideband

board:

BW = 0.80

* f

out

Measurement basics

Activated option

B160 / U160

20 40

Figure 3-13: Relationship between maximum usable I/Q bandwidth and output sample rate with and

Restricting the maximum bandwidth manually

By default, all installed bandwidth extension options are activated, allowing for the maximum bandwidth for measurements on the R&S FSW. However, sometimes the maximum bandwidth is not necessary. For example, due to the correlation of both parameters, high sample rates automatically lead to an extended analysis bandwidth. However, while a high sample rate can be necessary (for example due to postprocessing in an OFDM system), the wide bandwidth is not necessarily required.

RF-Input:

BW = 0.80

* f

out

without bandwidth extensions

100

120

140

160 180 200

Option B80 / U80

or deactivated

option B160 / U160

Option B40 / U40

Without BW

extension options

... 10000

Output sample

rate f

out

[MHz]

On the other hand, low sample rates lead to small usable I/Q bandwidths. To ensure the availability of the required bandwidth, the minimum required bandwidth for the specified sample rate can be selected (via remote command only).

Thus, if one of the bandwidth extension options is installed, the maximum bandwidth can be restricted manually to a value that can improve the measurement (see "Maxi-

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Sample rate and maximum usable I/Q bandwidth for RF input

mum Bandwidth" on page 87). In this case, the hardware of the "regular" RF path is

used, rather than the hardware required by the bandwidth extension options.

The following improvements can be achieved:

●

Longer measurement time for sample rates under 300 MHz

●

Data processing becomes up to 10 times faster.

●

Digital baseband output becomes available (with bandwidth extension options that do not support output).

General notes and restrictions

●

The memory extension option R&S FSW-B106 is only available together with the R&S FSW-B160 or B320 bandwidth extension options.

●

The memory extension option R&S FSW-B108 is only available together with the R&S FSW-B1200/-B2001/-B800R options.

●

The memory extension option R&S FSW-B124 is only available together with the R&S FSW-B4001/B6001/B8001 options.

●

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

3.5.3 R&S FSW without additional bandwidth extension options

Sample rate: 100 Hz - 20 GHz

Maximum I/Q bandwidth: 28 MHz

Table 3-4: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 28 MHz Proportional up to maximum 28 MHz

28 MHz to 20 GHz 28 MHz

MSRA operating mode

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

3.5.4 R&S FSW with I/Q bandwidth extension option B40 or U40

Sample rate: 100 Hz - 20 GHz

Maximum bandwidth: 40 MHz

Table 3-5: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 50 MHz Proportional up to maximum 40 MHz

50 MHz to 20 GHz 40 MHz

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3.5.5 R&S FSW with I/Q bandwidth extension option B80 or U80

Measurement basics

Sample rate and maximum usable I/Q bandwidth for RF input

MSRA operating mode

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

Sample rate: 100 Hz - 20 GHz

Maximum bandwidth: 80 MHz

Table 3-6: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 100 MHz Proportional up to maximum 80 MHz

100 MHz to 20 GHz 80 MHz

MSRA operating mode

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

3.5.6 R&S FSW with activated I/Q bandwidth extension option B160 or U160

Sample rate: 100 Hz - 20 GHz

Maximum bandwidth: 160 MHz

Table 3-7: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 200 MHz Proportional up to maximum 160 MHz

200 MHz to 20 GHz 160 MHz

Table 3-8: Maximum record length with activated I/Q bandwidth extension option B160 or U160

Sample rate Maximum record length

100 Hz to 200 MHz 440 Msamples

Notes and restrictions for R&S FSW-B160 or U160

●

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

220 Msamples

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3.5.7 R&S FSW with activated I/Q bandwidth extension option B320/U320

Measurement basics

Sample rate and maximum usable I/Q bandwidth for RF input

Table 3-9: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 400 MHz Proportional up to maximum 320 MHz

400 MHz to 20 GHz 320 MHz

Figure 3-14: Relationship between maximum usable I/Q bandwidth and output sample rate for active

Table 3-10: Maximum record length with activated I/Q bandwidth extension option B320 or U320

Sample rate Maximum record length

100 Hz to 200 MHz*) 440 Msamples

200 MHz to 468 MHz 470 Msamples * sample rate / 1GHz

468 MHz to 20 GHz 220 Msamples

*) for sample rates up to 200 MHz the I/Q bandwidth extension B320 is not used

R&S FSW-B320

With R&S FSW-B106 option: 1400 Msamples

With R&S FSW-B106 option: 1400 Msamples * sample rate / 1GHz

With R&S FSW-B106 option: 700 Msamples

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3.5.8 R&S FSW with activated I/Q bandwidth extension option B512

Measurement basics

Sample rate and maximum usable I/Q bandwidth for RF input

Notes and restrictions for R&S FSW-B320

●

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

The bandwidth extension option R&S FSW-B512 provides measurement bandwidths up to 512 MHz.

Table 3-11: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 600 MHz 0.8 * sample rate (up to maximum 512 MHz)

600 MHz to 20 GHz 512 MHz

Figure 3-15: Relationship between maximum usable I/Q bandwidth and output sample rate for active

Table 3-12: Maximum record length with activated I/Q bandwidth extension option R&S FSW-B512

Sample rate Maximum record length

100 Hz to 20 GHz 440 Msamples

R&S FSW-B512

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Notes and restrictions for R&S FSW-B512

●

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz and a maximum record length of 220 Msamples.

●

The memory extension options R&S FSW-B106/-B108/-B124 are not available together with the -B512 option.

Bandwidths between 480 MHz and 512 MHz with R&S FSW-B512 option

Note the irregular behavior of the relationshipt between the sample rate and the usable I/Q bandwidth for bandwidths between 480 MHz and 512 MHz with the -B512 options, depending on which setting you change.

For compatibility reasons, the common relationship is maintained for bandwidths ≤ 480 MHz:

Usable I/Q bandwidth = 0.8 * output sample rate

However, to make use of the maximum sample rate of 600 MHz at the maximum bandwidth of 512 MHz, there is an exception. If you change the bandwidth between 480 MHz and 500 MHz, the sample rate is adapted according to the relationship:

Output sample rate =

usable I/Q bandwidth / (500/600)

Output sample rate = usable I/Q bandwidth / 0.8333

When using option R&S FSW-B512R, if you change the bandwidth between 500 MHz and 512 MHz, the sample rate is adapted according to the relationship:

Output sample rate =

usable I/Q bandwidth / (512/600)

Output sample rate = usable I/Q bandwidth / 0.8533

On the other hand, if you decrease the sample rate under 600 MHz, the I/Q bandwidth is adapted according to the common relationship:

Usable I/Q bandwidth =

0.8 * output sample rate.

3.5.9 R&S FSW with activated I/Q bandwidth extension option B1200

The bandwidth extension option R&S FSW-B1200 provides measurement bandwidths up to 1200 MHz.

Table 3-13: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 600 MHz 0.8 * sample rate

600 MHz 0.8533 * sample rate (=512 MHz)

600 MHz to 1500 MHz 0.8 * sample rate *)

1500 MHz to 20 GHz 1200 MHz

*) Exception: for active digital I/Q 40G streaming output, a sample rate of 1200 MHz provides a maximum I/Q bandwidth of 1000 MHz

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Sample rate and maximum usable I/Q bandwidth for RF input

Figure 3-16: Relationship between maximum usable I/Q bandwidth and output sample rate for active

Table 3-14: Maximum record length with activated I/Q bandwidth extension option R&S FSW-B1200

Sample rate Maximum record length

100 Hz to 600 MHz 440 Msamples

600 MHz to 1250 MHz 480 Msamples * (sample rate / 1250 MHz); max. 440 Msamples

1250 MHz to 20 GHz max. 440 Msamples

R&S FSW-B1200

With R&S FSW-B108 option: max. 1800 Msamples

With R&S FSW-B108 option: 990 Msamples * (sample rate / 1250 MHz); max. 900 Msamples

With R&S FSW-B108 option: 900 Msamples * (sample rate / 1250 MHz); max. 900 Msamples

Notes and restrictions for R&S FSW-B1200

●

The memory extension option R&S FSW-B106 is not available together with the B1200 option.

●

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

●

When the R&S FSW-B1200 option is active, only an external trigger (or no trigger) is available.

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Sample rate and maximum usable I/Q bandwidth for RF input

Irregular behavior in bandwidths between 480 MHz and R&S FSW512 MHz with R&S FSW-B1200 option

Note that the B1200 bandwidth extension option has the same irregular behavior of the relationship between the sample rate and the usable I/Q bandwidth for bandwidths between 480 MHz and 512 MHz as the B512 option. The R&S FSW uses the same hardware for both options up to 512 MHz.

For compatibility reasons, the common relationship is maintained for bandwidths ≤ 480 MHz:

Output sample rate = usable I/Q bandwidth / 0.8

However, to make use of the maximum sample rate of 600 MHz at the maximum bandwidth of 500 MHz, there is an exception. If you change the bandwidth between 480 MHz and 500 MHz, the sample rate is adapted according to the relationship:

Output sample rate = usable I/Q bandwidth / (500/600)

Output sample rate = usable I/Q bandwidth / 0.8333

If you change the bandwidth between 500 MHz and 512 MHz, the sample rate is adapted according to the relationship:

Output sample rate =

usable I/Q bandwidth / (512/600)

Output sample rate =

usable I/Q bandwidth / 0.8533

If you increase the bandwidth above 512 MHz, the common relationship is maintained again:

Output sample rate = usable I/Q bandwidth / 0.8

On the other hand, if you set the sample rate to 600 MHz, the I/Q bandwidth is set to:

Output sample rate * 0.8533 = 512

MHz

However, if you decrease the sample rate under 600 MHz or increase the sample rate above 600 MHz, the I/Q bandwidth is adapted according to the common relation-

ship:

Usable I/Q bandwidth =

0.8 * output sample rate.

3.5.10 R&S FSW with activated I/Q bandwidth extension option B2001

The (internal) bandwidth extension option R&S FSW-B2001 provides measurement bandwidths up to 2 GHz, with no additional devices required.

Table 3-15: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

100 Hz to 600 MHz 0.8 * sample rate

600 MHz 0.8533 * sample rate (=512 MHz)

*) Exception: for active digital I/Q 40G streaming output, a sample rate of 1200 MHz provides a maximum I/Q bandwidth of 1000 MHz

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Sample rate and maximum usable I/Q bandwidth for RF input

Sample rate Maximum I/Q bandwidth

600 MHz to 2500 MHz 0.8 * sample rate *)

2500 MHz to 20 GHz 2000 MHz

*) Exception: for active digital I/Q 40G streaming output, a sample rate of 1200 MHz provides a maximum I/Q bandwidth of 1000 MHz

Usable I/Q bandwidth [MHz]

2000

1800

1600

1400

1200

I/Q bandwidths for RF input

Activated option

B2001

1000

800

600

512 480

400

200

250 500 750 1000

1250

RF-Input:

BW = 0.80 * f

1500 1750

out

2000

2250

2500

Output sample

10000

...

rate f

out

[MHz]

600

Figure 3-17: Relationship between maximum usable I/Q bandwidth and output sample rate for active

Table 3-16: Maximum record length with activated I/Q bandwidth extension option R&S FSW-B2001

Sample rate Maximum record length

100 Hz to 600 MHz 440 Msamples

600 MHz to 1250 MHz 440 Msamples * (sample rate / 1250 MHz); max. 900 Msamples

R&S FSW-B2001

With R&S FSW-B108 option: max. 1800 Msamples

With R&S FSW-B108 option: 900 Msamples * (sample rate / 1250 MHz); max. 900 Msamples

1250 MHz to 20 GHz 440 Msamples * (sample rate / 2500 MHz); max. 900 Msamples

With R&S FSW-B108 option: 900 Msamples * (sample rate / 1250 MHz); max. 900 Msamples

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Notes and restrictions for R&S FSW-B2001

●

The memory extension option R&S FSW-B106 is not available together with the B2001 option.

●

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 600 MHz.

●

When the R&S FSW-B2001 option is active, only an external trigger (or no trigger) is available.

Irregular behavior in bandwidths between 480 MHz and 512 MHz with R&S FSWB2001 option

Note that the B2001 bandwidth extension option has the same irregular behavior of the relationship between the sample rate and the usable I/Q bandwidth for bandwidths between 480 MHz and 512 MHz as the -B512 options. The R&S FSW uses the same hardware for both options up to 512 MHz.

For compatibility reasons, the common relationship is maintained for bandwidths ≤ 480 MHz:

Output sample rate = usable I/Q bandwidth / 0.8

Output sample rate =

If you change the bandwidth between 500 MHz and 512 MHz, the sample rate is adapted according to the relationship:

Output sample rate = usable I/Q bandwidth / (512/600)

Output sample rate =

If you increase the bandwidth above 512 MHz, the common relationship is maintained again:

Output sample rate =

On the other hand, if you set the sample rate to 600 MHz, the I/Q bandwidth is set to:

Output sample rate * 0.8533 = 512 MHz

However, if you decrease the sample rate under 600 MHz or increase the sample rate above 600 MHz, the I/Q bandwidth is adapted according to the common relation-

ship:

Usable I/Q bandwidth =

usable I/Q bandwidth / (500/600)

usable I/Q bandwidth / 0.8333

usable I/Q bandwidth / 0.8533

usable I/Q bandwidth / 0.8

0.8 * output sample rate.

3.5.11 R&S FSW with activated I/Q bandwidth extension option B2000

The bandwidth extension option R&S FSW-B2000 provides measurement bandwidths up to 2 GHz.

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Sample rate and maximum usable I/Q bandwidth for RF input

Table 3-17: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

10 kHz to 20 GHz Proportional up to maximum 2 GHz

Figure 3-18: Relationship between maximum usable I/Q bandwidth and output sample rate for active

R&S FSW-B2000

Notes and restrictions for R&S FSW-B2000

●

The memory extension options R&S FSW-B106/-B108/-B124 are not available together with the B2000 option.

●

If the R&S FSW-B2000 bandwidth extension option is active, MSRA operating mode is not available.

●

The maximum memory size, and thus record length, available for a single input channel can be reduced by half in the following cases:

– When using an external trigger in common B2000 mode, which uses another

channel on the oscilloscope. – In power splitter mode, which uses two input channels on the oscilloscope. For details, see the oscilloscope's data sheet and documentation.

For details on the power splitter mode, see the R&S FSW I/Q Analyzer and I/Q Input user manual.

3.5.12 R&S FSW with activated I/Q bandwidth extension option B5000

The bandwidth extension option R&S FSW-B5000 provides measurement bandwidths up to 5 GHz.

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Sample rate and maximum usable I/Q bandwidth for RF input

Table 3-18: Maximum I/Q bandwidth

Sample rate Maximum I/Q bandwidth

10 kHz to 20 GHz Proportional up to maximum 5 GHz

Figure 3-19: Relationship between maximum usable I/Q bandwidth and output sample rate for active

R&S FSW-B5000

Notes and restrictions for R&S FSW-B5000

●

The memory extension options R&S FSW-B106/-B108/-B124 are not available together with the B5000 option.

●

If the R&S FSW-B5000 bandwidth extension option is active, MSRA operating mode is not available.

●

The maximum memory size, and thus record length, available for a single input channel can be reduced by half in the following cases:

– When using an external trigger in common B5000 mode, which uses another

channel on the oscilloscope. – In power splitter mode, which uses two input channels on the oscilloscope. For details, see the oscilloscope's data sheet and documentation.

For details on the power splitter mode, see the R&S FSW I/Q Analyzer and I/Q Input user manual.

3.5.13 R&S FSW with activated I/Q bandwidth extension option B4001/

B6001/B8001

The (internal) bandwidth extension options R&S FSW-B4001/B6001/B8001 provide measurement bandwidths up to 4 GHz, 6 GHz or 8 GHz, respectively, with no additional devices required. The B4001 option is activated automatically for bandwidths

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Sample rate and maximum usable I/Q bandwidth for RF input

larger than 80 MHz, if installed. The B6001 and B8001 options are activated automatically for bandwidths larger than 80 MHz and center frequencies above 18 GHz, if installed.

The memory extension options R&S FSW-B106/-B108 are not available together with the B4001/B6001/B8001 options.

Table 3-19: Maximum I/Q bandwidth

Option Sample rate Maximum I/Q bandwidth

B4001 100 Hz to 5500 MHz 0.8 * sample rate

5500 MHz to 20 GHz 4400 MHz

B6001 100 Hz to 8000 MHz 0.8 * sample rate

8000 MHz to 20 GHz 6400 MHz

B8001 100 Hz to 10390 MHz 0.8 * sample rate

10390 MHz to 20 GHz 8312 MHz

Usable I/Q bandwidth [MHz]

8312

8000

7000

6400

6000

5000

4400

4000

3000

2000

1000

1000 2000 3000 4000

Figure 3-20: Relationship between maximum usable I/Q bandwidth and output sample rate for active

Table 3-20: Maximum record length with activated I/Q bandwidth extension option R&S FSW-B4001/

R&S FSW-B4001/B6001/B8001

B6001/B8001

I/Q bandwidths for RF input

RF-Input:

BW = 0.80 * f

out

5500 10390

5000

6000 7000

8000

9000

10000

Activated option

B8001

Activated option

B6001

Activated option

B4001

Output sample

rate f

out

...

max

[MHz]

Sample rate Maximum record length

100 Hz to 100 MHz 440 Msamples

100 MHz to 20 GHz 1039 Msamples

100 MHz to 5.32 GHz 1039 Msamples

With R&S FSW-B124 option: max. 5600 Msamples

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3.6 OFDM VSA in MSRA operating mode

Measurement basics

OFDM VSA in MSRA operating mode

Sample rate Maximum record length

5.32 GHz to 10.64 GHz 1039 Msamples With R&S FSW-B124 option: max. 6440 Msamples

10.64 GHz to 20 GHz 1039 Msamples With R&S FSW-B124 option: max. 2800 Msamples

Notes and restrictions for R&S FSW-B4001/B6001/B8001

●

In MSRA operating mode, the MSRA primary is restricted to a sample rate of 200 MHz and a maximum bandwidth of 80 MHz.

●

If a R&S FSW-B4001/B6001/B8001 option is active, only an external trigger (or no trigger) is available.

The R&S FSW OFDM VSA application can also be used to analyze data in MSRA operating mode.

In MSRA operating mode, only the MSRA primary actually captures data; the MSRA applications receive an extract of the captured data for analysis, referred to as the application data. For the R&S FSW OFDM VSA application in MSRA operating mode, the application data range is defined by the same settings used to define the signal capture in Signal and Spectrum Analyzer mode. In addition, a capture offset can be defined, i.e. an offset from the start of the captured data to the start of the application data for vector signal analysis. The "Capture Buffer" displays show the application data of the R&S FSW OFDM VSA application in MSRA mode.

Data coverage for each active application

Generally, if a signal contains multiple data channels for multiple standards, separate applications are used to analyze each data channel. Thus, it is of interest to know which application is analyzing which data channel. The MSRA primary display indicates the data covered by each application, restricted to the channel bandwidth used by the corresponding standard, by vertical blue lines labeled with the application name. The R&S FSW OFDM VSA application supports several standards, but the standard used by the currently analyzed data is not known. Thus, the "Symbol Rate" defined in the "Signal Description" settings is used to approximate the channel bandwidth.

Analysis interval

However, the individual result displays of the application need not analyze the complete data range. The data range that is actually analyzed by the individual result display is referred to as the analysis interval.

In the R&S FSW OFDM VSA application, the analysis interval is automatically determined according to the evaluation range or result range settings, as in Signal and Spectrum Analyzer mode. The currently used analysis interval (in seconds, related to capture buffer start) is indicated in the window header for each result display.

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Analysis line

A frequent question when analyzing multi-standard signals is how each data channel is correlated (in time) to others. Thus, an analysis line has been introduced. The analysis line is a common time marker for all MSRA secondary applications. It can be positioned in any MSRA secondary application or the MSRA primary and is then adjusted in all other secondary applications. Thus, you can easily analyze the results at a specific time in the measurement in all secondary applications and determine correlations.

If the analysis interval of the secondary application contains the marked point in time, the line is indicated in all time-based result displays, such as time, symbol, slot or bit diagrams. By default, the analysis line is displayed. However, you can hide it from view manually. In all result displays, the "AL" label in the window title bar indicates whether the analysis line lies within the analysis interval or not:

●

orange "AL": the line lies within the interval

●

white "AL": the line lies within the interval, but is not displayed (hidden)

●

no "AL": the line lies outside the interval

For details on the MSRA operating mode, see the R&S

FSW MSRA User Manual.

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4 Configuring OFDM VSA measurements

Configuring OFDM VSA measurements

When you activate a measurement channel for the R&S FSW OFDM VSA application, a OFDM VSA measurement for the input signal is started automatically with the default configuration. The "OFDM VSA" menu is displayed and provides access to the most important configuration functions.

General R&S FSW functions

The application-independent functions for general tasks on the R&S FSW are also available for the R&S FSW OFDM VSA application and are described in the R&S FSW user manual. In particular, the application supports the following functionality:

●

Data management

●

Test report functionality

●

General software preferences and information

●

Fast access panel

Importing and exporting I/Q data

The I/Q data to be evaluated in the R&S FSW OFDM VSA application cannot only be measured by the R&S FSW OFDM VSA application itself, it can also be imported to the application, provided it has the correct format. Furthermore, the evaluated I/Q data from the R&S FSW OFDM VSA application can be exported for further analysis in external applications.

The import and export functions are available in the "Save/Recall" menu which is displayed when you select the "Save" or "Open" icon in the toolbar.

For details on importing and exporting I/Q data, see the R&S FSW base unit user manual.

● Configuration overview............................................................................................59

● Signal description....................................................................................................60

● Input, output and frontend settings..........................................................................64

● Trigger settings....................................................................................................... 80

● Data acquisition.......................................................................................................85

● Sweep settings........................................................................................................89

● Burst search............................................................................................................90

● Result ranges..........................................................................................................91

● Synchronization, demodulation and tracking.......................................................... 91

● Adjusting settings automatically..............................................................................95

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4.1 Configuration overview

Configuring OFDM VSA measurements

Configuration overview

Access: [Meas Config] > "Overview"

Throughout the measurement configuration, an overview of the most important currently defined settings is provided in the "Overview".

Figure 4-1: Configuration "Overview" for the R&S FSW OFDM VSA application

In addition to the main measurement settings, the "Overview" provides quick access to the main settings dialog boxes. Thus, you can easily configure an entire measurement channel from input over processing to evaluation by stepping through the dialog boxes as indicated in the "Overview".

In particular, the "Overview" provides quick access to the following configuration dialog boxes (listed in the recommended order of processing):

1. Signal description See Chapter 4.2, "Signal description", on page 60

2. Input/Frontend See Chapter 4.3, "Input, output and frontend settings", on page 64

3. Trigger See Chapter 4.4, "Trigger settings", on page 80

4. Data acquisition See Chapter 4.5, "Data acquisition", on page 85

5. Burst search See Chapter 4.7, "Burst search", on page 90

6. Result range

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Signal description

See Chapter 4.8, "Result ranges", on page 91

7. Synchronization and demodulation settings See Chapter 4.9, "Synchronization, demodulation and tracking", on page 91

8. Tracking See Chapter 4.9, "Synchronization, demodulation and tracking", on page 91

9. Result configuration See Chapter 6.1, "Result configuration", on page 123

To configure settings

► Select any button in the "Overview" to open the corresponding dialog box.

Select a setting in the channel bar (at the top of the measurement channel tab) to change a specific setting.

Preset Channel............................................................................................................. 60

Specific Settings for...................................................................................................... 60

Preset Channel

Select the "Preset Channel" button in the lower left-hand corner of the "Overview" to restore all measurement settings in the current channel to their default values.

Note: Do not confuse the "Preset Channel" button with the [Preset] key, which restores the entire instrument to its default values and thus closes all channels on the R&S FSW (except for the default channel)!

Remote command:

SYSTem:PRESet:CHANnel[:EXEC] on page 150

Specific Settings for

The channel can contain several windows for different results. Thus, the settings indicated in the "Overview" and configured in the dialog boxes vary depending on the selected window.

Select an active window from the "Specific Settings for" selection list that is displayed in the "Overview" and in all window-specific configuration dialog boxes.

The "Overview" and dialog boxes are updated to indicate the settings for the selected window.

4.2 Signal description

Access: "Overview" > "Signal Description"

You must describe the expected input signal so that the R&S FSW OFDM VSA application can compare the measured signal to the expected reference signal. You can load an existing configuration file, or create one interactively using a wizard for the current input signal (see Chapter 5, "Creating a configuration file using the wizard", on page 97).

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Signal description

The R&S FSW OFDM VSA application provides some sample files for I/Q input data and configuration files in the C:\R_S\INSTR\USER\demo\OFDM-VSA directory.

Use Configuration File...................................................................................................61

Load Configuration File.................................................................................................61

Create Configuration File.............................................................................................. 62

Export Data (to Create Config File on Other PC)..........................................................62

DFT-s-OFDM / SC-FDMA:Transform Precoding...........................................................62

RF Upconversion: Phase Compensation......................................................................62

FFT Size........................................................................................................................63

Cyclic Prefix Length...................................................................................................... 63

Preamble Symbol Characteristics: Block Length.......................................................... 63

Frame Start Offset.........................................................................................................63

Advanced Cyclic Prefix Configuration...........................................................................63

Different cyclic prefix lengths.........................................................................................63

└ Cyclic prefix definition per range (Symbols / Samples)...................................64

Use Configuration File

Determines whether the configuration from the currently loaded file is used for the measurement. Alternatively, you can configure the OFDM signal manually.

Remote command:

CONFigure:SYSTem:CFILe on page 154

Load Configuration File

Opens a file selection dialog box to select the configuration (.XML) file for the measurement.

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Signal description

Note: Configuration files with more than 100 different modulation types cannot be loaded.

Remote command:

MMEMory:LOAD:CFGFile on page 156

Create Configuration File

Opens a wizard that helps you create a new configuration file interactively. See Chap-

ter 5, "Creating a configuration file using the wizard", on page 97.

Export Data (to Create Config File on Other PC)

Exports the current settings to a .K96_wizv file. Use this input file to create a configuration file using the wizard on another PC.

DFT-s-OFDM / SC-FDMA:Transform Precoding

DFT-s-OFDM and SC-FDMA are different names for a method that can be applied to lower the crest factor of the RF signal.

For DFT-s-OFDM, an additional digital Fourier transformation (DFT) is included in the transmitter's signal processing stage, referred to as precoding. If this method is used by the input signal, enable the "Transform Precoding" option to decode the precoding transformation using an iDFT. The R&S FSW OFDM VSA application tries to detect contiguous groups of data cells for each OFDM symbol and decode them using an inverse DFT. Zero cells are ignored.

If "Transform Precoding" is enabled, define how to process OFDM symbols that contain "Don't Care" and pilot cells:

"Ignore pilot/don't care" enabled:

OFDM symbols that contain pilot or "Don't Care" cells are decoded, but these cells are ignored.

"Ignore pilot/don't care" disabled:

OFDM symbols that contain a pilot or a "Don't Care" cell are skipped and not decoded.

If precoding is enabled, take special care when editing the configuration file. Make sure that all cells are allocated correctly, that is:

●

No cell is falsely allocated as a data cell.

●

All data cells are allocated as data cells.

Otherwise, the iDFT parameters (length, start, stop) are not correct and all data cells in that OFDM symbol are demodulated inaccurately.

Remote command:

CONFigure:TPRecoding on page 155 CONFigure:TPRecoding:IGNore on page 155

RF Upconversion: Phase Compensation

For example, in 5G uplink signals, the phase shifts from one OFDM symbol to the next. In this case, the R&S FSW OFDM VSA application must revert the phase compensation that is applied to the signal during RF upconversion. The phase compensation is based on a fixed frequency, which can either be the center frequency, or you can define the frequency for the shift manually.

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Signal description

Remote command:

CONFigure:RFUC:STATe on page 152 CONFigure:RFUC:FZERo:MODE on page 151 CONFigure:RFUC:FZERo:FREQuency on page 151

FFT Size

Defines the useful length of an OFDM symbol in the time domain as the number of samples. This setting determines the number of samples used as input for each FFT calculation.

This setting is not available if a configuration file is active (see "Use Configuration File" on page 61). In this case, the FFT length defined in the file is displayed for reference only.

Remote command:

CONFigure[:SYMBol]:NFFT on page 154

Cyclic Prefix Length

Defines the length of the cyclic prefix (CP) area between two OFDM symbols in samples. The cyclic prefix area defines the guard interval and is expected to contain a copy of the samples at the end of the OFDM symbol.

The cyclic prefix length must be smaller than or equal to the "FFT Size" on page 63.

Preamble Symbol Characteristics: Block Length

Instead of using the cyclic prefix for the time synchronization, the R&S FSW OFDM VSA application can also use a preamble that contains repetitive blocks of samples (if available in the signal). This setting specifies the length of one data block within the repetitive preamble as a number of samples.

Remote command:

CONFigure:PREamble:BLENgth on page 150

Frame Start Offset

Specifies the time offset from the preamble start to the actual frame start as a number of samples.

Remote command:

CONFigure:PREamble:FOFFset on page 151

Advanced Cyclic Prefix Configuration

Additional settings for non-conventional cyclic prefixes are displayed when you select the "Advanced" button, and hidden when you select "Basic".

By default, "Conventional Mode" is assumed, that is: each OFDM symbol has the same cyclic prefix length. Thus, only the basic cyclic prefix settings are shown.

Remote command:

CONFigure[:SYMBol]:GUARd:MODE on page 152

Different cyclic prefix lengths

Some OFDM signals change their cyclic prefix over time (e.g. 802.11ac). This setting defines the behavior in such a case.

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Input, output and frontend settings

"Periodic"

"Non-Periodic"

Remote command:

CONFigure[:SYMBol]:GUARd:PERiodic on page 153

One "slot" that consists of the two defined ranges is repeated over and over until the number of symbols specified by the result range parameter is reached. The ranges are repeated periodically, first range 1, then range 2, then range 1, etc.

Figure 4-2: Non-Conventional cyclic prefix case: Periodic mode

A fixed preamble has a different cyclic prefix length than the rest of the frame (e.g. WLAN 802.11ac signals). In this case, the length of the second range is extended until the end of the demodulated frame. Therefore, the length of the second range cannot be specified in this case.

Figure 4-3: Non-Conventional cyclic prefix case: Non-Periodic mode

Cyclic prefix definition per range (Symbols / Samples) ← Different cyclic prefix lengths

For each range, configure the number of symbols the cyclic prefix length is applied to, and the length of the cyclic prefix as a number of samples.

For non-periodic cyclic prefixes, the length of the second range cannot be specified. It is extended to the end of the demodulated frame.

Remote command:

CONFigure[:SYMBol]:GUARd:NSYMbols<cp> on page 153 CONFigure[:SYMBol]:NGUard<cp> on page 154

4.3 Input, output and frontend settings

Access: "Overview" > "Input/Frontend"

Or: [INPUT/OUTPUT]

The R&S FSW can evaluate signals from different input sources.

The frequency and amplitude settings represent the frontend of the measurement setup.

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4.3.1 Input settings

Configuring OFDM VSA measurements

Input, output and frontend settings

● Input settings...........................................................................................................65

● Output settings........................................................................................................70

● Frequency settings..................................................................................................74

● Amplitude settings...................................................................................................75

Access: "Overview" > "Input/Frontend" > "Input"

Or: [INPUT/OUTPUT]

Some settings are also available in the "Amplitude" tab of the "Amplitude" dialog box, see "Input Settings" on page 77.

Input from other sources

The R&S FSW OFDM VSA application can also process input from the following optional sources:

●

I/Q input files

●

External mixer

●

External frontend

●

Digital Baseband (I/Q) Interface (R&S FSW-B17)

●

Analog Baseband Interface (R&S FSW-B71)

●

Baseband oscilloscope input (R&S FSW-B2071)

●

2 GHz / 5 GHz bandwidth extension (R&S FSW-B2000/B5000)

●

Probes

For details, see the R&S FSW I/Q Analyzer and I/Q Input user manual.

● Radio frequency input............................................................................................. 65

● Settings for input from I/Q data files........................................................................69

4.3.1.1 Radio frequency input

Access: "Overview" > "Input/Frontend" > "Input" > "Radio Frequency"

Or: [INPUT/OUTPUT] > "Input Source Config" > "Input" > "Radio Frequency"

The default input source for the R&S FSW is the radio frequency.

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RF input protection

The RF input connector of the R&S FSW must be protected against signal levels that exceed the ranges specified in the data sheet. Therefore, the R&S FSW is equipped with an overload protection mechanism for DC and signal frequencies up to 30 MHz. This mechanism becomes active as soon as the power at the input mixer exceeds the specified limit. It ensures that the connection between RF input and input mixer is cut off.

When the overload protection is activated, an error message is displayed in the status bar ("INPUT OVLD"), and a message box informs you that the RF input was disconnected. Furthermore, a status bit (bit 3) in the STAT:QUES:POW status register is set. In this case, you must decrease the level at the RF input connector and then close the message box. Then measurement is possible again. Reactivating the RF input is also possible via the remote command INPut<ip>:ATTenuation:PROTection:RESet.

Radio Frequency State................................................................................................. 66

Input Coupling...............................................................................................................67

Impedance.................................................................................................................... 67

Direct Path.................................................................................................................... 68

High Pass Filter 1 to 3 GHz...........................................................................................68

YIG-Preselector.............................................................................................................68

Input Connector.............................................................................................................68

Radio Frequency State

Activates input from the "RF Input" connector. For R&S FSW85 models with two input connectors, you must define which input

source is used for each measurement channel.

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Input, output and frontend settings

If an external frontend is active, select the connector the external frontend is connected to. You cannot use the other RF input connector simultaneously for the same channel. However, you can configure the use of the other RF input connector for another active channel at the same time.

"Input 1"

1.00 mm RF input connector for frequencies up to 85 GHz (90 GHz

with option R&S FSW-B90G) "Input 2" Remote command:

INPut<ip>:SELect on page 160 INPut<ip>:TYPE on page 161

Input Coupling

The RF input of the R&S FSW can be coupled by alternating current (AC) or direct current (DC).

For an active external frontend, input coupling is always DC. AC coupling blocks any DC voltage from the input signal. AC coupling is activated by

default to prevent damage to the instrument. Very low frequencies in the input signal can be distorted.

However, some specifications require DC coupling. In this case, you must protect the instrument from damaging DC input voltages manually. For details, refer to the data sheet.

Remote command:

INPut<ip>:COUPling on page 157

Impedance

The R&S FSW has an internal impedance of 50 Ω. However, some applications use other impedance values. To match the impedance of an external application to the impedance of the R&S FSW, an impedance matching pad can be inserted at the input. If the type and impedance value of the used matching pad is known to the R&S FSW, it can convert the measured units accordingly so that the results are calculated correctly.

This function is not available for input from the optional "Digital Baseband" interface. Not all settings are supported by all R&S FSW applications.

1.85 mm RF input connector for frequencies up to 67 GHz

The impedance conversion does not affect the level of the output signals (such as IF, video, demod, digital I/Q output).

Ω"

"50 "75Ω"

"User"

(Default:) no conversion takes place

The 50 Ω input impedance is transformed to a higher impedance

using a 75 Ω adapter of the selected "Pad Type": "Series-R" (default)

or "MLP" (Minimum Loss Pad)

The 50 Ω input impedance is transformed to a user-defined impe-

dance value according to the selected "Pad Type": "Series-R"

(default) or "MLP" (Minimum Loss Pad)

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Input, output and frontend settings

Remote command:

INPut<ip>:IMPedance on page 159 INPut<ip>:IMPedance:PTYPe on page 160

Direct Path

Enables or disables the use of the direct path for small frequencies. In spectrum analyzers, passive analog mixers are used for the first conversion of the

input signal. In such mixers, the LO signal is coupled into the IF path due to its limited isolation. The coupled LO signal becomes visible at the RF frequency 0 Hz. This effect is referred to as LO feedthrough.

To avoid the LO feedthrough the spectrum analyzer provides an alternative signal path to the A/D converter, referred to as the direct path. By default, the direct path is selected automatically for RF frequencies close to zero. However, this behavior can be disabled. If "Direct Path" is set to "Off", the spectrum analyzer always uses the analog mixer path.

For an active external frontend, the direct path is always used automatically for frequencies close to zero.

"Auto"

"Off" Remote command:

INPut<ip>:DPATh on page 158

(Default) The direct path is used automatically for frequencies close

to zero.

The analog mixer path is always used.

High Pass Filter 1 to 3 GHz

Activates an additional internal highpass filter for RF input signals from 1 GHz to 3 GHz. This filter is used to remove the harmonics of the analyzer to measure the harmonics for a DUT, for example.

This function requires an additional hardware option. Note: For RF input signals outside the specified range, the high-pass filter has no

effect. For signals with a frequency of approximately 4 GHz upwards, the harmonics are suppressed sufficiently by the YIG-preselector, if available.)

Remote command:

INPut<ip>:FILTer:HPASs[:STATe] on page 158

YIG-Preselector

Enables or disables the YIG-preselector, if available on the R&S FSW. Note: Note that the YIG-preselector is active only on frequencies greater than 8 GHz.

Therefore, switching the YIG-preselector on or off has no effect if the frequency is below that value.

To use the optional 90 GHz frequency extension (R&S FSW-B90G), the YIG-preselector must be disabled.

Remote command:

INPut<ip>:FILTer:YIG[:STATe] on page 159

Input Connector

Determines which connector the input data for the measurement is taken from.

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Input, output and frontend settings

"RF" "RF Probe"

Remote command:

INPut<ip>:CONNector on page 157

4.3.1.2 Settings for input from I/Q data files

Access: "Overview" > "Input/Frontend" > "Input Source" > "I/Q File"

Or: [INPUT/OUTPUT] > "Input Source Config" > "Input Source" > "I/Q File"

(Default:) The "RF Input" connector

The "RF Input" connector with an adapter for a modular probe

This setting is only available if a probe is connected to the "RF Input"

connector.

It is not available for an active external frontend.

I/Q Input File State........................................................................................................ 69

Select I/Q data file.........................................................................................................69

File Repetitions............................................................................................................. 70

I/Q Input File State

Enables input from the selected I/Q input file. If enabled, the application performs measurements on the data from this file. Thus,

most measurement settings related to data acquisition (attenuation, center frequency, measurement bandwidth, sample rate) cannot be changed. The measurement time can only be decreased to perform measurements on an extract of the available data only.

Note: Even when the file input is disabled, the input file remains selected and can be enabled again quickly by changing the state.

Remote command:

INPut<ip>:SELect on page 160

Select I/Q data file

Opens a file selection dialog box to select an input file that contains I/Q data.

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The I/Q data file must be in one of the following supported formats:

.iq.tar

●

.iqw

●

.csv

●

.mat

●

.wv

●

.aid

● For details on formats, see the R&S FSW I/Q Analyzer and I/Q Input user manual.

Note: Only a single data stream or channel can be used as input, even if multiple streams or channels are stored in the file.

Note: For some file formats that do not provide the sample rate and measurement time or record length, you must define these parameters manually. Otherwise the traces are not visible in the result displays.

The default storage location for I/Q data files is C:\R_S\INSTR\USER. Remote command:

INPut<ip>:FILE:PATH on page 162

File Repetitions

Determines how often the data stream is repeatedly copied in the I/Q data memory to create a longer record. If the available memory is not sufficient for the specified number of repetitions, the largest possible number of complete data streams is used.

Remote command:

TRACe:IQ:FILE:REPetition:COUNt on page 163

4.3.2 Output settings

Access: [INPUT/OUTPUT] > "OUTPUT Config"

The R&S FSW OFDM VSA application can provide output to special connectors for other devices.

For details on connectors, refer to the R&S FSW Getting Started manual, "Front / Rear Panel View" chapters.

Output settings can be configured via the [Input/Output] key or in the "Output" dialog box.

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Input, output and frontend settings

Data Output...................................................................................................................71

Noise Source Control....................................................................................................72

Trigger 2/3.....................................................................................................................72

└ Output Type.................................................................................................... 73

└ Level..................................................................................................... 73

└ Pulse Length.........................................................................................73

└ Send Trigger.........................................................................................73

Data Output

Defines the type of signal available at one of the output connectors of the R&S FSW. "IF"

"2ND IF"

The measured IF value is provided at the IF/VIDEO/DEMOD output

connector.

For bandwidths up to 80 MHZ, the IF output is provided at the speci-

fied "IF Out Frequency".

If an optional bandwidth extension R&S FSW-B160/-B320/-B512 is

used, the measured IF value is available at the "IF WIDE OUTPUT"

connector. The frequency at which this value is output is determined

automatically. It is displayed as the "IF Wide Out Frequency". For

details on the used frequencies, see the data sheet.

This setting is not available for bandwidths larger than 512 MHz.

The measured IF value is provided at the "IF OUT 2 GHz/ IF OUT

5 GHz " output connector, if available, at a frequency of 2 GHz and

with a bandwidth of 2 GHz. The availability of this connector depends

on the instrument model.

This setting is not available if the optional 2 GHz / 5 GHz bandwidth

extension (R&S FSW-B2000/B5000) is active.

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Input, output and frontend settings

Remote command:

OUTPut<up>:IF[:SOURce] on page 235

Noise Source Control

Enables or disables the 28 V voltage supply for an external noise source connected to the "Noise source control / Power sensor") connector. By switching the supply voltage for an external noise source on or off in the firmware, you can enable or disable the device as required.

External noise sources are useful when you are measuring power levels that fall below the noise floor of the R&S FSW itself, for example when measuring the noise level of an amplifier.

In this case, you can first connect an external noise source (whose noise power level is known in advance) to the R&S FSW and measure the total noise power. From this value, you can determine the noise power of the R&S FSW. Then when you measure the power level of the actual DUT, you can deduct the known noise level from the total power to obtain the power level of the DUT.

Remote command:

DIAGnostic:SERVice:NSOurce on page 235

Trigger 2/3

The trigger input and output functionality depends on how the variable "Trigger Input/ Output" connectors are used.

"Trigger 1" "Trigger 2"

"Trigger 1" is input only.

Defines the usage of the variable "Trigger Input/Output" connector on

the front panel

(not available for R&S FSW85 models with 2 RF input connectors) "Trigger 3"

"Input"

Defines the usage of the variable "Trigger 3 Input/Output" connector

on the rear panel

The signal at the connector is used as an external trigger source by

the R&S FSW. Trigger input parameters are available in the "Trigger"

dialog box.

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"Output"

Remote command:

OUTPut<up>:TRIGger<tp>:DIRection on page 236

Output Type ← Trigger 2/3

Type of signal to be sent to the output "Device Trig-

gered" "Trigger

Armed"

"User Defined"

Remote command:

OUTPut<up>:TRIGger<tp>:OTYPe on page 237

Level ← Output Type ← Trigger 2/3

Defines whether a high (1) or low (0) constant signal is sent to the trigger output connector (for "Output Type": "User Defined".

The trigger pulse level is always opposite to the constant signal level defined here. For example, for "Level" = "High", a constant high signal is output to the connector until you select the Send Trigger function. Then, a low pulse is provided.

The R&S FSW sends a trigger signal to the output connector to be

used by connected devices.

Further trigger parameters are available for the connector.

(Default) Sends a trigger when the R&S FSW triggers.

Sends a (high level) trigger when the R&S FSW is in "Ready for trig-

ger" state.

This state is indicated by a status bit in the STATus:OPERation reg-

ister (bit 5), as well as by a low-level signal at the "AUX" port (pin 9).

Sends a trigger when you select the "Send Trigger" button.

In this case, further parameters are available for the output signal.

Remote command:

OUTPut<up>:TRIGger<tp>:LEVel on page 236

Pulse Length ← Output Type ← Trigger 2/3

Defines the duration of the pulse (pulse width) sent as a trigger to the output connector. Remote command:

OUTPut<up>:TRIGger<tp>:PULSe:LENGth on page 238

Send Trigger ← Output Type ← Trigger 2/3

Sends a user-defined trigger to the output connector immediately. Note that the trigger pulse level is always opposite to the constant signal level defined

by the output Level setting. For example, for "Level" = "High", a constant high signal is output to the connector until you select the "Send Trigger" function. Then, a low pulse is sent.

Which pulse level is sent is indicated by a graphic on the button.

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4.3.3 Frequency settings

Configuring OFDM VSA measurements

Input, output and frontend settings

Remote command:

OUTPut<up>:TRIGger<tp>:PULSe:IMMediate on page 238

Access: [FREQ] > "Frequency Config"

Center Frequency......................................................................................................... 74

Center Frequency Stepsize...........................................................................................74

Frequency Offset...........................................................................................................74

Center Frequency

Defines the center frequency of the signal in Hertz. f

and span

max

depend on the instrument and are specified in the data sheet.

min

Remote command:

[SENSe:]FREQuency:CENTer on page 212

Center Frequency Stepsize

Defines the step size when scrolling through center frequency values. The step size can be set to a predefined value, or it can be manually set to a user-defined value.

"Auto"

"Manual"

The step size is set to the default value:

●

using the rotary knob: 100 kHz

●

using the arrow keys: 1 MHz

Defines a user-defined step size for the center frequency. Enter the

step size in the "Value" field. Remote command:

[SENSe:]FREQuency:CENTer:STEP:AUTO on page 212 [SENSe:]FREQuency:CENTer:STEP on page 212

Frequency Offset

Shifts the displayed frequency range along the x-axis by the defined offset.

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4.3.4 Amplitude settings

Configuring OFDM VSA measurements

Input, output and frontend settings

This parameter has no effect on the instrument's hardware, on the captured data, or on data processing. It is simply a manipulation of the final results in which absolute frequency values are displayed. Thus, the x-axis of a spectrum display is shifted by a constant offset if it shows absolute frequencies. However, if it shows frequencies relative to the signal's center frequency, it is not shifted.

A frequency offset can be used to correct the display of a signal that is slightly distorted by the measurement setup, for example.

The allowed values range from -1 THz to 1 THz. The default setting is 0 Hz. Note: In MSRA mode, this function is only available for the MSRA primary. Remote command:

[SENSe:]FREQuency:OFFSet on page 212

Access: [AMPT] > "Amplitude Config"

Amplitude settings affect the signal power or error levels.

Note that amplitude settings are not window-specific, as opposed to the scaling and unit settings.

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Reference Level............................................................................................................76

└ Shifting the Display (Offset)............................................................................ 76

└ Setting the Reference Level Automatically (Auto Level).................................77

Input Settings................................................................................................................ 77

└ Preamplifier.....................................................................................................77

└ Input Coupling.................................................................................................77

Impedance.................................................................................................................... 78

RF Attenuation.............................................................................................................. 78

└ Attenuation Mode / Value................................................................................78

Optimization.................................................................................................................. 79

Using Electronic Attenuation.........................................................................................79

Reference Level

The reference level can also be used to scale power diagrams; the reference level is then used for the calculation of the maximum on the y-axis.

Since the hardware of the R&S FSW is adapted according to this value, it is recommended that you set the reference level close above the expected maximum signal level. Thus you ensure an optimum measurement (no compression, good signal-tonoise ratio).

Note: Note that for input from the External Mixer (R&S FSW-B21) the maximum refer- ence level also depends on the conversion loss; see the R&S FSW base unit user manual for details.

For an active external frontend, the reference level refers to the RF input at the external frontend, not the levels at the RF input of the R&S FSW.

Remote command:

DISPlay[:WINDow<n>][:SUBWindow<w>]:TRACe<t>:Y[:SCALe]:RLEVel

on page 213

Shifting the Display (Offset) ← Reference Level

Defines an arithmetic level offset. This offset is added to the measured level. In some result displays, the scaling of the y-axis is changed accordingly.

Define an offset if the signal is attenuated or amplified before it is fed into the R&S FSW so the application shows correct power results. All displayed power level results are shifted by this value.

The setting range is ±200 dB in 0.01 dB steps. Note, however, that the internal reference level (used to adjust the hardware settings to

the expected signal) ignores any "Reference Level Offset". Thus, it is important to keep in mind the actual power level the R&S FSW must handle. Do not rely on the displayed reference level (internal reference level = displayed reference level - offset).

Remote command:

DISPlay[:WINDow<n>][:SUBWindow<w>]:TRACe<t>:Y[:SCALe]:RLEVel: OFFSet on page 213

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Input, output and frontend settings

Setting the Reference Level Automatically (Auto Level) ← Reference Level

Automatically determines a reference level which ensures that no overload occurs at the R&S FSW for the current input data. At the same time, the internal attenuators and the preamplifier (for analog baseband input: the full-scale level) are adjusted. As a result, the signal-to-noise ratio is optimized, while signal compression and clipping are minimized.

To determine the required reference level, a level measurement is performed on the R&S FSW.

If necessary, you can optimize the reference level further. Decrease the attenuation level manually to the lowest possible value before an overload occurs, then decrease the reference level in the same way.

Remote command:

[SENSe:]ADJust:LEVel on page 214

Input Settings

Some input settings affect the measured amplitude of the signal, as well. For information on other input settings, see Chapter 4.3.1, "Input settings", on page 65.

Preamplifier ← Input Settings

If the (optional) internal preamplifier hardware is installed, a preamplifier can be activated for the RF input signal.

You can use a preamplifier to analyze signals from DUTs with low output power. Note: If an optional external preamplifier is activated, the internal preamplifier is auto-

matically disabled, and vice versa. For an active external frontend, a preamplifier is not available. For all R&S FSW models except for R&S FSW85, the following settings are available:

"Off" "15 dB" "30 dB" For R&S FSW85 models, the input signal is amplified by 30 dB if the preamplifier is

activated. Remote command:

INPut<ip>:GAIN:STATe on page 217 INPut<ip>:GAIN[:VALue] on page 217

Input Coupling ← Input Settings

The RF input of the R&S FSW can be coupled by alternating current (AC) or direct current (DC).

For an active external frontend, input coupling is always DC. AC coupling blocks any DC voltage from the input signal. AC coupling is activated by

default to prevent damage to the instrument. Very low frequencies in the input signal can be distorted.

However, some specifications require DC coupling. In this case, you must protect the instrument from damaging DC input voltages manually. For details, refer to the data sheet.

Deactivates the preamplifier. The RF input signal is amplified by about 15 dB. The RF input signal is amplified by about 30 dB.

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Input, output and frontend settings

Remote command:

INPut<ip>:COUPling on page 157

Impedance

This function is not available for input from the optional "Digital Baseband" interface. Not all settings are supported by all R&S FSW applications.

The impedance conversion does not affect the level of the output signals (such as IF, video, demod, digital I/Q output).

"50Ω"

(Default:) no conversion takes place

"75Ω"

"User"

Remote command:

INPut<ip>:IMPedance on page 159 INPut<ip>:IMPedance:PTYPe on page 160

RF Attenuation

Defines the mechanical attenuation for RF input. This function is not available for input from the optional R&S Digital Baseband Inter-

face.

Attenuation Mode / Value ← RF Attenuation

The RF attenuation can be set automatically as a function of the selected reference level (Auto mode). Automatic attenuation ensures that no overload occurs at the RF Input connector for the current reference level. It is the default setting.

By default and when no (optional) electronic attenuation is available, mechanical attenuation is applied.

In "Manual" mode, you can set the RF attenuation in 1 dB steps (down to 0 dB). Other entries are rounded to the next integer value. The range is specified in the data sheet. If the defined reference level cannot be set for the defined RF attenuation, the reference level is adjusted accordingly and the warning "limit reached" is displayed.

NOTICE! Risk of hardware damage due to high power levels. When decreasing the attenuation manually, ensure that the power level does not exceed the maximum level allowed at the RF input, as an overload can lead to hardware damage.

Remote command:

INPut<ip>:ATTenuation on page 214 INPut<ip>:ATTenuation:AUTO on page 215

The 50 Ω input impedance is transformed to a higher impedance using a 75 Ω adapter of the selected "Pad Type": "Series-R" (default) or "MLP" (Minimum Loss Pad)

The 50 Ω input impedance is transformed to a user-defined impedance value according to the selected "Pad Type": "Series-R" (default) or "MLP" (Minimum Loss Pad)

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Input, output and frontend settings

Optimization

Selects the priority for signal processing after the RF attenuation has been applied. This function is only available under the following conditions:

●

One of the following options that provide a separate wideband processing path in the R&S FSW is installed: – Bandwidth extension R&S FSW-B160/-B320 Extension Board 1, Revision 2 or

higher – Bandwidth extension R&S FSW-B512, B1200, B2001, B4001, B6001, or B8001 – Real-time option R&S FSW-B160R

(Currently not supported for K161R, B512R and B800R/K800RE)

●

An I/Q bandwidth higher than 80 MHz is used. (Only in this case the wideband path is used.)

●

The optional "Digital Baseband" interface is not active.

"Low distortion"

(Default:) Optimized for low distortion by avoiding intermodulation

"Low noise"

Remote command:

INPut<ip>:ATTenuation:AUTO:MODE on page 215

Optimized for high sensitivity and low noise levels If this setting is selected, "Low noise" is indicated in the channel information bar.

Using Electronic Attenuation

If the (optional) Electronic Attenuation hardware is installed on the R&S FSW, you can also activate an electronic attenuator.

In "Auto" mode, the settings are defined automatically; in "Manual" mode, you can define the mechanical and electronic attenuation separately.

For an active external frontend, electronic attenuation is not available. Note: Electronic attenuation is not available for stop frequencies (or center frequencies

in zero span) above 15 GHz. In "Auto" mode, RF attenuation is provided by the electronic attenuator as much as possible to reduce the amount of mechanical switching required. Mechanical attenuation can provide a better signal-to-noise ratio, however.

When you switch off electronic attenuation, the RF attenuation is automatically set to the same mode (auto/manual) as the electronic attenuation was set to. Thus, the RF attenuation can be set to automatic mode, and the full attenuation is provided by the mechanical attenuator, if possible.

The electronic attenuation can be varied in 1 dB steps. If the electronic attenuation is on, the mechanical attenuation can be varied in 5 dB steps. Other entries are rounded to the next lower integer value.

For the R&S FSW85, the mechanical attenuation can be varied only in 10 dB steps. If the defined reference level cannot be set for the given attenuation, the reference

level is adjusted accordingly and the warning "limit reached" is displayed in the status bar.

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4.4 Trigger settings

Configuring OFDM VSA measurements

Trigger settings

Remote command:

INPut<ip>:EATT:STATe on page 216 INPut<ip>:EATT:AUTO on page 216 INPut<ip>:EATT on page 215

Access: "Overview" > "Signal Capture" > "Trigger"

Or: [TRIG] > "Trigger Config"

The trigger settings define the beginning of a measurement.

For step-by-step instructions on configuring triggered measurements, see the R&S FSW user manual.

Trigger Source...............................................................................................................81

└ Free Run.........................................................................................................81

└ External Trigger 1/2/3..................................................................................... 81

└ External Channel 3......................................................................................... 81

└ IF Power..........................................................................................................82

└ Baseband Power.............................................................................................82

└ I/Q Power........................................................................................................82

└ RF Power........................................................................................................82

└ Digital I/Q........................................................................................................ 83

Trigger Level................................................................................................................. 83

Trigger Offset................................................................................................................ 83

Hysteresis..................................................................................................................... 83

Drop-Out Time...............................................................................................................84

Coupling........................................................................................................................84

Slope.............................................................................................................................84

Trigger Holdoff...............................................................................................................84

Capture Offset...............................................................................................................84

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Trigger settings

Trigger Source

Defines the trigger source. If a trigger source other than "Free Run" is set, "TRG" is displayed in the channel bar and the trigger source is indicated.

Remote command:

TRIGger[:SEQuence]:SOURce on page 221

Free Run ← Trigger Source

No trigger source is considered. Data acquisition is started manually or automatically and continues until stopped explicitly.

Remote command: TRIG:SOUR IMM, see TRIGger[:SEQuence]:SOURce on page 221

External Trigger 1/2/3 ← Trigger Source

Data acquisition starts when the TTL signal fed into the specified input connector meets or exceeds the specified trigger level.

(See "Trigger Level" on page 83). Note: The "External Trigger 1" softkey automatically selects the trigger signal from the

"TRIGGER 1 INPUT" connector on the front panel. For details, see the "Instrument Tour" chapter in the R&S FSW Getting Started manual.

"External Trigger 1"

Trigger signal from the "TRIGGER 1 INPUT" connector.

"External Trigger 2"

Trigger signal from the "TRIGGER 2 INPUT / OUTPUT" connector. For R&S FSW85 models, "Trigger 2" is not available due to the second RF input connector on the front panel.

"External Trigger 3"

Trigger signal from the "TRIGGER 3 INPUT / OUTPUT" connector on the rear panel.

Remote command:

TRIG:SOUR EXT, TRIG:SOUR EXT2 TRIG:SOUR EXT3

See TRIGger[:SEQuence]:SOURce on page 221

External Channel 3 ← Trigger Source

Data acquisition starts when the signal fed into the "Ch3" input connector on the oscilloscope meets or exceeds the specified trigger level.

Note: In previous firmware versions, the external trigger was connected to the "Ch2" input on the oscilloscope. As of firmware version R&S FSW 2.30, the "Ch3" input on the oscilloscope must be used!

This trigger source is only available if the optional 2 GHz / 5 GHz bandwidth extension (R&S FSW-B2000/B5000) is active (see R&S FSW I/Q Analyzer and I/Q Input User Manual).

Note: Since the external trigger uses a second channel on the oscilloscope, the maximum memory size, and thus record length, available for the input channel 1 may be reduced by half. For details, see the oscilloscope's data sheet and documentation.

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Trigger settings

Remote command: TRIG:SOUR EXT, see TRIGger[:SEQuence]:SOURce on page 221

IF Power ← Trigger Source

The R&S FSW starts capturing data as soon as the trigger level is exceeded around the third intermediate frequency.

For frequency sweeps, the third IF represents the start frequency. The trigger threshold depends on the defined trigger level, as well as on the RF attenuation and preamplification. A reference level offset, if defined, is also considered. The trigger bandwidth at the intermediate frequency depends on the RBW and sweep type. For details on available trigger levels and trigger bandwidths, see the instrument data sheet.

For measurements on a fixed frequency (e.g. zero span or I/Q measurements), the third IF represents the center frequency.

This trigger source is only available for RF input. The available trigger levels depend on the RF attenuation and preamplification. A refer-

ence level offset, if defined, is also considered. For details on available trigger levels and trigger bandwidths, see the data sheet. Remote command:

TRIG:SOUR IFP, see TRIGger[:SEQuence]:SOURce on page 221

Baseband Power ← Trigger Source

Defines triggering on the baseband power (for baseband input via the optional "Digital Baseband" interface or the optional "Analog Baseband" interface).

Remote command: TRIG:SOUR BBP, see TRIGger[:SEQuence]:SOURce on page 221

I/Q Power ← Trigger Source

Triggers the measurement when the magnitude of the sampled I/Q data exceeds the trigger threshold.

Remote command: TRIG:SOUR IQP, see TRIGger[:SEQuence]:SOURce on page 221

RF Power ← Trigger Source

Defines triggering of the measurement via signals which are outside the displayed measurement range.

For this purpose, the instrument uses a level detector at the first intermediate frequency.

The resulting trigger level at the RF input depends on the RF attenuation and preamplification. For details on available trigger levels, see the instrument's data sheet.

Note: If the input signal contains frequencies outside of this range (e.g. for fullspan measurements), the measurement can be aborted. A message indicating the allowed input frequencies is displayed in the status bar.

A "Trigger Offset", "Trigger Polarity" and "Trigger Holdoff" (to improve the trigger stability) can be defined for the RF trigger, but no "Hysteresis".

Remote command: TRIG:SOUR RFP, see TRIGger[:SEQuence]:SOURce on page 221

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Configuring OFDM VSA measurements

Trigger settings

Digital I/Q ← Trigger Source

For applications that process I/Q data, such as the I/Q Analyzer or optional applications, and only if the optional "Digital Baseband" interface is available:

Defines triggering of the measurement directly via the "LVDS" connector. In the selection list, specify which general-purpose bit ("GP0" to "GP5") provides the trigger data.

Note: If the Digital I/Q enhanced mode is used, i.e. the connected device supports transfer rates up to 200 Msps, only the general-purpose bits "GP0" and "GP1" are available as a Digital I/Q trigger source.

The following table describes the assignment of the general-purpose bits to the LVDS connector pins.

Table 4-1: Assignment of general-purpose bits to LVDS connector pins

Bit LVDS pin

GP0 SDATA4_P - Trigger1

GP1 SDATA4_P - Trigger2

GP2

GP3

GP4

GP5

: not available for Digital I/Q enhanced mode

SDATA0_P - Reserve1

SDATA4_P - Reserve2

SDATA0_P - Marker1

SDATA4_P - Marker2

Remote command: TRIG:SOUR GP0, see TRIGger[:SEQuence]:SOURce on page 221

Trigger Level

Defines the trigger level for the specified trigger source. For details on supported trigger levels, see the instrument data sheet. Remote command:

TRIGger[:SEQuence]:LEVel[:EXTernal<port>] on page 219

Trigger Offset

Defines the time offset between the trigger event and the start of the measurement.

Offset > 0: Start of the measurement is delayed

Offset < 0: Measurement starts earlier (pretrigger)

Remote command:

TRIGger[:SEQuence]:HOLDoff[:TIME] on page 219

Hysteresis

Defines the distance in dB to the trigger level that the trigger source must exceed before a trigger event occurs. Setting a hysteresis avoids unwanted trigger events caused by noise oscillation around the trigger level.

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Configuring OFDM VSA measurements

Trigger settings

This setting is only available for "IF Power" trigger sources. The range of the value is between 3 dB and 50 dB with a step width of 1 dB.

Remote command:

TRIGger[:SEQuence]:IFPower:HYSTeresis on page 219

Drop-Out Time

Defines the time that the input signal must stay below the trigger level before triggering again.

Remote command:

TRIGger[:SEQuence]:DTIMe on page 218

Coupling

If the selected trigger source is "IF Power" or "External Channel 3", you can configure the coupling of the external trigger to the oscilloscope.

This setting is only available if the optional 2 GHz bandwidth extension is active. "DC 50 Ω"

"DC 1 MΩ"

"AC"

Remote command:

TRIGger[:SEQuence]:OSCilloscope:COUPling on page 211

Slope

For all trigger sources except time, you can define whether triggering occurs when the signal rises to the trigger level or falls down to it.

When using the optional 2 GHz / 5 GHz bandwidth extension (R&S FSW-B2000/ B5000) with an IF power trigger, only rising slopes can be detected.

Remote command:

TRIGger[:SEQuence]:SLOPe on page 221

Trigger Holdoff

Defines the minimum time (in seconds) that must pass between two trigger events. Trigger events that occur during the holdoff time are ignored.

Remote command:

TRIGger[:SEQuence]:IFPower:HOLDoff on page 219

Direct connection with 50 Ω termination, passes both DC and AC components of the trigger signal.

Direct connection with 1 MΩ termination, passes both DC and AC components of the trigger signal.

Connection through capacitor, removes unwanted DC and very lowfrequency components.

Capture Offset

This setting is only available for secondary applications in MSRA operating mode. It has a similar effect as the trigger offset in other measurements: it defines the time offset between the capture buffer start and the start of the extracted secondary application data.

In MSRA mode, the offset must be a positive value, as the capture buffer starts at the trigger time = 0.

For details on the MSRA operating mode, see the R&S FSW MSRA User Manual.

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4.5 Data acquisition

Configuring OFDM VSA measurements

Data acquisition

Remote command:

[SENSe:]MSRA:CAPTure:OFFSet on page 267

Configure how data is to be acquired in the "Data Acquisition" dialog box.

MSRA operating mode

In MSRA operating mode, only the MSRA primary channel actually captures data from the input signal. The data acquisition settings for the OFDM VSA application in MSRA mode define the application data extract and analysis interval.

For details on the MSRA operating mode, see the R&S FSW MSRA User Manual.

Capture Time.................................................................................................................86

Capture Length............................................................................................................. 86

Sample Rate................................................................................................................. 86

Oversampling / Capture Sample Rate.......................................................................... 86

Maximum Bandwidth.....................................................................................................87

Swap I/Q....................................................................................................................... 87

Filter State.....................................................................................................................88

6-dB Bandwidth.............................................................................................................88

50-dB Bandwidth...........................................................................................................88

Highpass Filter State.....................................................................................................88

6-dB Bandwidth.............................................................................................................88

50-dB Bandwidth...........................................................................................................89

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Configuring OFDM VSA measurements

Data acquisition

Capture Time

Specifies the duration (and therefore the amount of data) to be captured in the capture buffer. If the capture time is too short, demodulation will fail. In particular, if the result length does not fit in the capture buffer, demodulation will fail.

Remote command:

[SENSe:]SWEep:TIME on page 225

Capture Length

Defines the number of samples to be captured during each measurement. The required Capture Time is adapted accordingly.

A maximum of 8 000 000 samples can be captured. Remote command:

[SENSe:]SWEep:LENGth on page 225

Sample Rate

Defines the I/Q data sample rate of the R&S FSW OFDM VSA application used for demodulation.

Note that the sample rate in the R&S FSW OFDM VSA application must correspond to the OFDM system sample rate, otherwise demodulation can fail.

Remote command:

TRACe:IQ:SRATe on page 226

Oversampling / Capture Sample Rate

By default, the R&S FSW OFDM VSA application captures data with a usable I/Q bandwidth that is 0.8 * sample rate.

(See Chapter 3.5, "Sample rate and maximum usable I/Q bandwidth for RF input", on page 40)

However, for some signals and measurements, a higher bandwidth is required. In this case, you can force the R&S FSW OFDM VSA application to capture with twice the sample rate, which is referred to as capture oversampling.

Oversampling is not available in the following cases:

●

A channel filter is enabled (see "Filter State" on page 88). In this case, an oversampling factor of 2 is applied automatically.

●

The defined Sample Rate is higher than half the maximum sample rate the R&S FSW supports.

The actual "Capture Sample Rate", that is: the rate with which the R&S FSW OFDM VSA application samples data, is calculated as:

Sample Rate * Oversampling factor

If you are analyzing data from an input file, the "Capture Sample Rate" indicates the rate with which the R&S FSW OFDM VSA application initially processes the data in the file.

In MSRA operating mode, only the MSRA primary channel actually captures data from the input signal. In this case, the "Capture Sample Rate" indicates the rate with which the R&S FSW OFDM VSA application receives data from the primary application.

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Data acquisition

"2x"

An oversampling of 2 is applied. The sample rate with which the R&S FSW OFDM VSA application captures data is twice the system sample rate.

"Off"

No oversampling is applied, the capture sample rate of the R&S FSW OFDM VSA application and the system sample rate are identical.

Remote command:

[SENSe:]CAPTure:OVERsampling on page 224

Maximum Bandwidth

Defines the maximum bandwidth to be used by the R&S FSW for I/Q data acquisition. Which options are available depends on which bandwidth extension options are installed.

This setting is only available if a bandwidth extension option greater than 160 MHz is installed on the R&S FSW. Otherwise the maximum bandwidth is determined automatically.

"Auto"

(Default:) All installed bandwidth extension options are enabled. The currently available maximum bandwidth is allowed. Note that using bandwidth extension options greater than 160 MHz may cause more spurious effects.

"80 MHz"

Restricts the analysis bandwidth to a maximum of 80 MHz. The bandwidth extension options greater than 160 MHz are disabled.

"160 MHz"

Restricts the analysis bandwidth to a maximum of 160 MHz. The bandwidth extension option for 320 MHz is disabled. (Not available or required if other bandwidth extension options larger than 320 MHz are installed.)

"512 MHz"

Restricts the analysis bandwidth to a maximum of 512 MHz. Larger bandwidth extension options are disabled.

"1200 MHz"

Restricts the analysis bandwidth to a maximum of 1200 MHz. Larger bandwidth extension options are disabled.

Remote command:

TRACe:IQ:WBANd[:STATe] on page 226 TRACe:IQ:WBANd:MBWidth on page 227

Swap I/Q

Activates or deactivates the inverted I/Q modulation. If the I and Q parts of the signal from the DUT are interchanged, the R&S FSW can do the same to compensate for it.

On I and Q signals are interchanged

Inverted sideband, Q+j*I

Off I and Q signals are not interchanged

Normal sideband, I+j*Q

Remote command:

[SENSe:]SWAPiq on page 224

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Data acquisition

Filter State

Defines whether a channel filter - and a highpass filter, if active - is applied to the I/Q data before OFDM demodulation.

Remote command:

INPut<ip>:FILTer:CHANnel[:LPASs][:STATe] on page 224

6-dB Bandwidth

Configures the bandwidth of the channel filter at which an attenuation of 6 dB is reached (see Figure 4-4). The filter bandwidth cannot be higher than the current Sam-

ple Rate. If necessary, the filter bandwidth is adapted to the current sample rate.

Figure 4-4: Definition of filter bandwidths

Remote command:

INPut<ip>:FILTer:CHANnel[:LPASs]:SDBBw on page 223

50-dB Bandwidth

Configures the 50-dB bandwidth of the channel filter. The 50-dB bandwidth is the bandwidth at which the filter reaches an attenuation of 50 dB (see Figure 4-4). This bandwidth must always be larger than the "6-dB Bandwidth" on page 88. If necessary, the 50-dB bandwidth is adapted to the current 6-dB bandwidth.

Remote command:

INPut<ip>:FILTer:CHANnel[:LPASs]:FDBBw on page 223

Highpass Filter State

Activates or deactivates an additional internal highpass filter. Remote command:

INPut<ip>:FILTer:CHANnel:HPASs[:STATe] on page 223

6-dB Bandwidth

Configures the bandwidth of the high pass filter at which an attenuation of 6 dB is reached (see Figure 4-4). The filter bandwidth cannot be higher than the current 6-dB

Bandwidth of the channel filter. If necessary, the filter bandwidth is adapted to the

same value.

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4.6 Sweep settings

Configuring OFDM VSA measurements

Sweep settings

Remote command:

INPut<ip>:FILTer:CHANnel:HPASs:SDBBw on page 222

50-dB Bandwidth

Indicates the 50-dB bandwidth of the high pass filter. The 50-dB bandwidth is the bandwidth at which the filter reaches an attenuation of 50 dB (see Figure 4-4). This bandwidth must always be smaller than the 6-dB Bandwidth of the high pass filter.

The 50-dB bandwidth cannot be defined manually. It is automatically determined according to the relation between the 6-dB bandwidth and the 50-dB bandwidth of the channel filter (see 6-dB Bandwidth and 50-dB Bandwidth).

Remote command:

INPut<ip>:FILTer:CHANnel:HPASs:FDBBw? on page 222

Access: [Sweep]

The sweep settings define how often data from the input signal is acquired and then evaluated.

Continuous Sweep / Run Cont......................................................................................89

Single Sweep / Run Single............................................................................................89

Refresh..........................................................................................................................90

Statistic Config / Max No of Frames to Analyze............................................................90

Continuous Sweep / Run Cont

After triggering, starts the measurement and repeats it continuously until stopped. This is the default setting.

While the measurement is running, the "Continuous Sweep" softkey and the [RUN CONT] key are highlighted. The running measurement can be aborted by selecting the highlighted softkey or key again. The results are not deleted until a new measurement is started.

Note: Sequencer. If the Sequencer is active, the "Continuous Sweep" softkey only controls the sweep mode for the currently selected channel. However, the sweep mode only takes effect the next time the Sequencer activates that channel, and only for a channel-defined sequence. In this case, a channel in continuous sweep mode is swept repeatedly. Furthermore, the [RUN CONT] key controls the Sequencer, not individual sweeps. [RUN CONT] starts the Sequencer in continuous mode.

For details on the Sequencer, see the R&S FSW User Manual. Remote command:

INITiate<n>:CONTinuous on page 240

Single Sweep / Run Single

While the measurement is running, the "Single Sweep" softkey and the [RUN SINGLE] key are highlighted. The running measurement can be aborted by selecting the highlighted softkey or key again.

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Burst search

Note: Sequencer. If the Sequencer is active, the "Single Sweep" softkey only controls the sweep mode for the currently selected channel. However, the sweep mode only takes effect the next time the Sequencer activates that channel, and only for a channel-defined sequence. In this case, the Sequencer sweeps a channel in single sweep mode only once. Furthermore, the [RUN SINGLE] key controls the Sequencer, not individual sweeps. [RUN SINGLE] starts the Sequencer in single mode.

If the Sequencer is off, only the evaluation for the currently displayed channel is updated.

For details on the Sequencer, see the R&S FSW User Manual. Remote command:

INITiate<n>[:IMMediate] on page 240

Refresh

Repeats the evaluation of the data currently in the capture buffer without capturing new data.

Remote command:

INITiate<n>:REFResh on page 240

Statistic Config / Max No of Frames to Analyze

Defines the maximum number of OFDM frames from the current capture buffer to be included in analysis.

If a configuration file is available, the contents of the file determine the frame. If no file is available, a single result range is considered a frame.

Remote command:

[SENSe:]DEMod:FORMat:MAXFrames on page 228

4.7 Burst search

Access: "Overview" > "Burst Search"

Or: "Meas Setup" > "Burst Search"

During a burst search, the capture buffer is searched for bursts that comply with the signal description. If no bursts are detected, the entire capture buffer is considered to be a single burst. A list of the detected bursts is passed on to the next processing stage.

See also Chapter 3.4, "OFDM measurement", on page 37.

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4.8 Result ranges

Configuring OFDM VSA measurements

Synchronization, demodulation and tracking

Burst Search State

Activates or deactivates a burst search. Remote command:

[SENSe:]DEMod:FORMat:BURSt on page 227

The result range is an extract from the capture buffer and defines the data basis used for further analysis.

Statistic Config / Max No of Frames to Analyze............................................................91

Result Length................................................................................................................91

Statistic Config / Max No of Frames to Analyze

Defines the maximum number of OFDM frames from the current capture buffer to be included in analysis.

If a configuration file is available, the contents of the file determine the frame. If no file is available, a single result range is considered a frame.

Remote command:

[SENSe:]DEMod:FORMat:MAXFrames on page 228

Result Length

Configures the number of OFDM symbols per frame to be analyzed. Note that this is not the maximum, but a precise number. If this number is higher than the actual number of symbols found in the signal, the result is not considered a frame, and not analyzed.

Note: If a loaded configuration file contains a <DefaultResultLength> entry, the specified value is used as the default result length for the current measurement setup.

Remote command:

[SENSe:]DEMod:FORMat:NOFSymbols on page 228

4.9 Synchronization, demodulation and tracking

Access: "Overview" > "Sync / Demod"/"Tracking"

Or: "Meas Setup" > "Sync / Demod"/"Tracking"

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Synchronization, demodulation and tracking

The following settings determine how the input signal is synchronized, demodulated, and tracked.

Time Synchronization

Parameter Estimation....................................................................................................92

Modulation Detection.................................................................................................... 93

Synchronization Thresholds..........................................................................................93

└ Minimum Time Sync Metric.............................................................................93

└ Minimum Frame Sync Metric.......................................................................... 94

Phase Tracking............................................................................................................. 94

Timing Tracking.............................................................................................................94

Level Tracking...............................................................................................................94

Channel Compensation.................................................................................................94

FFT Shift relative to Cyclic Prefix Length......................................................................95

Maximum Carrier Offset................................................................................................95

Cyclic Delay.................................................................................................................. 95

Time Synchronization

Specifies the synchronization method in the time domain. "Cyclic Prefix"

"Preamble" Remote command:

[SENSe:]DEMod:TSYNc on page 231

....................................................................................................92

The cyclic prefix method performs a correlation of the cyclic prefix with the end of the FFT interval.

The preamble method searches for the repetitive preamble blocks.

Parameter Estimation

Defines which parts of the OFDM signal are used for the parameter estimation. This setting is only available if a configuration file is loaded and active (see "Use Con-

figuration File" on page 61). In manual configuration mode without a configuration file,

no parameter estimation is performed. "Pilot-Aided"

Uses only the predefined pilot cells for parameter estimation.

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Synchronization, demodulation and tracking

"Pilot And Data-Aided"

Uses both pilots and detected data cells for an additional synchronization step.

Remote command:

[SENSe:]DEMod:FSYNc on page 230

Modulation Detection

Specifies how the modulation of the data cells is detected. The R&S FSW OFDM VSA application can use the modulation configured in the con-

figuration file for each cell. Alternatively, the R&S FSW OFDM VSA application tries to detect the used modulation

automatically based on the available modulation types (which are also defined in the configuration file). For automatic detection, the R&S FSW OFDM VSA application analyzes the modulation type per carrier or per symbol.

This setting is only available if a configuration file is loaded and active (see "Use Con-

figuration File" on page 61).

"Configuration File"

"Symbolwise"

"Carrierwise"

Remote command:

[SENSe:]DEMod:MDETect on page 230

The modulation format configured for the cell is used. Note that if the actual modulation of a constellation point differs from the configured modulation for the cell, the EVM is increased.

A common modulation format for all data cells within one OFDM symbol is determined.

A common modulation format for all data cells within one OFDM carrier is determined.

Synchronization Thresholds

If you require particular reliability in synchronization results, define thresholds for the success of synchronization required to calculate results. The current reliability is indicated in the Signal Flow.

High thresholds are useful if several similar, but not identical frames, must be distinguished. In this case, it is important that the application synchronizes only to the correct frame to obtain correct results.

On the other hand, if the signal quality is poor, only a low level of reliability in synchronization can be achieved. In this case, high thresholds can prevent the application from evaluating any frames at all.

For details, see Chapter 3.4.1, "Synchronization block", on page 38.

Minimum Time Sync Metric ← Synchronization Thresholds

Defines the minimum reliability required for time synchronization. Values between 0 and 1 are allowed, where:

●

0: low threshold, very poor reliability is sufficient to synchronize successfully (always fulfilled)

●

1: high threshold, time synchronization must be absolutely reliable to be successful (only possible for ideal signal).

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Synchronization, demodulation and tracking

The default value is 0.5, that means: for reliability of 50 %, time synchronization is successful.

Remote command:

[SENSe:]DEMod:THReshold:TIME on page 230

Minimum Frame Sync Metric ← Synchronization Thresholds

Defines the minimum correlation rate of the CP or preamble for frame synchronization to be successful.

Values between 0 and 1 are allowed, where:

●

0: low threshold, a very poor correlation is sufficient to synchronize successfully (always fulfilled)

●

1: high threshold, correlation must be very precise for frame synchronization to be successful (only possible for ideal signal).

The default value is 0.5, that means: for a correlation of 50 %, frame synchronization is successful.

Remote command:

[SENSe:]DEMod:THReshold:FRAMe on page 231

Phase Tracking

Defines whether phase tracking is used to improve the signal quality. The compensation is done on a per-symbol basis.

This setting is only available if a configuration file is loaded and active (see "Use Con-

figuration File" on page 61).

Remote command:

SENSe:TRACking:PHASe on page 232

Timing Tracking

Defines whether timing tracking is used to improve the signal quality (for sample clock deviations). The compensation is done on a per-symbol basis.

This setting is only available if a configuration file is loaded and active (see "Use Con-

figuration File" on page 61).

Remote command:

SENSe:TRACking:TIME on page 232

Level Tracking

Defines whether level tracking is used to improve the signal quality (for power level deviations). The compensation is done on a per-symbol basis.

This setting is only available if a configuration file is loaded and active (see "Use Con-

figuration File" on page 61).

Remote command:

SENSe:TRACking:LEVel on page 232

Channel Compensation

Defines whether channel tracking is used to improve the signal quality (for the channel transfer function). The compensation is done on a per-carrier basis.

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Adjusting settings automatically

This setting is only available if a configuration file is loaded and active (see "Use Con-

figuration File" on page 61).

Remote command:

[SENSe:]COMPensate:CHANnel on page 229

FFT Shift relative to Cyclic Prefix Length

Defines the starting point of the FFT relative to the cyclic prefix length. Thus, you can shift the FFT start sample within the guard interval. Shifting is useful if relevant parts of the channel impulse response fall outside the cyclic prefix interval.

A value of 0 is the first sample; a value of 1.0 is the last sample of the cyclic prefix.

Remote command:

[SENSe:]DEMod:FFTShift on page 229

Maximum Carrier Offset

The R&S FSW OFDM VSA application can compensate for possible carrier offsets. However, searching for offsets slows down the measurement. This setting defines the range of carriers in which the R&S FSW OFDM VSA application searches for an offset.

To eliminate the search for carrier offset altogether, set the number of carriers to 0. In this case, the center frequency offset must be less than half the carrier distance to obtain useful results.

This setting is only available if a configuration file is loaded and active (see "Use Con-

figuration File" on page 61).

Remote command:

[SENSe:]DEMod:COFFset on page 229

Cyclic Delay

Defines a cyclic shift of the FFT values for each OFDM symbol on the transmitter end before adding the cyclic prefix. This known shift should be compensated in the receiver to get a correct channel phase response.

Remote command:

[SENSe:]DEMod:CDD on page 229

4.10 Adjusting settings automatically

Access: "Auto Set"

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Adjusting settings automatically

Depending on the R&S FSW, some settings can be adjusted by the instrument automatically according to the current measurement settings. To do so, a measurement is performed.

To activate the automatic adjustment of a setting from the R&S FSW, select the corresponding function in the "Auto Set" menu or in the configuration dialog box for the setting, where available.

Adjusting settings automatically during triggered measurements

When you select an auto adjust function, a measurement is performed to determine the optimal settings. If you select an auto adjust function for a triggered measurement, you are asked how the R&S FSW should behave:

●

(Default:) The measurement for adjustment waits for the next trigger

●

The measurement for adjustment is performed without waiting for a trigger. The trigger source is temporarily set to "Free Run". After the measurement is completed, the original trigger source is restored. The trigger level is adjusted as follows for "IF Power" and "RF Power" triggers: Trigger level = Reference level - 15 dB

Remote command:

[SENSe:]ADJust:CONFigure:TRIGger on page 234

Setting the Reference Level Automatically (Auto Level)

To determine the required reference level, a level measurement is performed on the R&S FSW.

Remote command:

[SENSe:]ADJust:LEVel on page 214

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5 Creating a configuration file using the wiz-

Creating a configuration file using the wizard

Understanding the R&S FSW-K96 Configuration File Wizard display

ard

The R&S FSW-K96 Configuration File Wizard (referred to as wizard here) is a tool that supports you in defining the configuration of your OFDM signal directly in the R&S FSW OFDM VSA application.

The R&S FSW OFDM VSA application has to know the configuration of the OFDM system to be able to demodulate an OFDM signal correctly. By configuration, we refer to the complete description of the OFDM system:

●

The number of subcarriers (i.e. the FFT size)

●

The number of symbols

●

The number of samples in the cyclic prefix (also referred to as guard length)

●

The position (carrier number, symbol number) of the: – Pilot symbols – Data symbols – Zero symbols – "Do not care" symbols

●

The modulation format of the data symbols (e.g. QPSK, 16QAM etc.)

●

The I/Q values of the pilot symbols

●

Optional: the definition of the preamble

This section describes how to generate the OFDM system configuration file in the R&S FSW OFDM VSA application for the current input signal.

The R&S FSW OFDM VSA application provides some sample files for I/Q input data and configuration files in the C:\R_S\INSTR\USER\demo\OFDM-VSA directory.

The R&S FSW-K96 Configuration File Wizard is provided with the R&S FSW OFDM VSA application firmware and stored on the instrument.

It is available from the Windows "Start" menu.

● Understanding the R&S FSW-K96 Configuration File Wizard display.................... 97

● Configuration steps............................................................................................... 105

● Reference of wizard menu functions.....................................................................112

● Example: creating a configuration file from an input signal...................................115

5.1 Understanding the R&S FSW-K96 Configuration File Wizard display

The following figure shows the R&S FSW-K96 Configuration File Wizard user interface. All different areas are labeled. They are explained in more detail in the following sections.

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Understanding the R&S FSW-K96 Configuration File Wizard display

1 2 3 4

Figure 5-1: Elements of the wizard user interface

1 = Menu functions (see Chapter 5.3, "Reference of wizard menu functions", on page 112) 2 = Progress indicator (see Chapter 5.2, "Configuration steps", on page 105) 3 = Constellation view 4 = Access to wizard help (see Chapter 5.3.4, "Help", on page 115) 5 = General signal information 6 = Matrix view

● General signal information...................................................................................... 98

● Constellation view................................................................................................... 99

● Matrix view............................................................................................................ 101

5.1.1 General signal information

General information on the configured signal is provided here for reference. Some values are derived from the configuration settings in the R&S FSW OFDM VSA application, others are generated by the wizard. The values displayed here are also included in the generated configuration file. If specified in the description, some values are shown in the "Signal Description" dialog box when you load the file in the R&S FSW OFDM VSA application.

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Understanding the R&S FSW-K96 Configuration File Wizard display

Number of Carriers........................................................................................................99

Number of Symbols.......................................................................................................99

Cyclic Prefix Length...................................................................................................... 99

System Name................................................................................................................99

System Description....................................................................................................... 99

Number of Carriers

Indicates the number of subcarriers used by the signal. This value corresponds to the

"FFT Size" on page 63.

Number of Symbols

The number of OFDM symbols corresponds to the result length configured in the "Result Range" settings in the R&S FSW OFDM VSA application (see "Result Length" on page 91).

Cyclic Prefix Length

The cyclic prefix length must be smaller than or equal to the "FFT Size" on page 63.

System Name

Defines the name of the stored configuration file. The default name is MyData. You can change the name in the "Settings" (see Chapter 5.3.3, "Settings", on page 114).

System Description

Provides a description of the signal configured in the file. By default, the following main characteristics are included:

●

Number of Carriers

●

Number of Symbols

●

Cyclic Prefix Length

If you deactivate the "Default" setting, you can overwrite the text with any other.

5.1.2 Constellation view

The "Constellation View" shows the constellation points (= I/Q values) for the OFDM cells in the defined result range. Using this view, you can assign the measured constellation points to specific cell types for the allocation matrix in the configuration file.

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Understanding the R&S FSW-K96 Configuration File Wizard display

Figure 5-2: Constellation View

Selection tool

Sets the cursor action to selection mode. All cells in the selection area are highlighted in color. The Selection Mode / Zoom Mode indicator shows which color is used. Any subsequent functions are applied to the selected cells.

Click in the diagram and move the cursor, holding the mouse button, to display a dotted rectangle and define the selection area.

Press the [Shift] key and click in the diagram to extend the selection to neighboring symbols.

Press the [CTRL] key and click in the diagram to add further (non-neighboring) points to the existing selection. Click the same points again to deselect them.

Zoom

Sets the cursor action to zoom mode. Click in the diagram and move the cursor, holding the mouse button, to display a rectangle and define the zoom area. The zoomed area is enlarged in the display. Repeat the action to zoom in further.

The Selection Mode / Zoom Mode indicator above the diagram shows that zoom mode is active.

To change the cursor function and stop zooming, select Selection tool.

Zoom Off

Displays the diagram in its original size.

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