Find us at www.keysight.com Page 1 Virtual Lab Program: Chapter 4 Digital Modulation Waveforms PathWave System Design (SystemVue) Introduction Keysight Technologies’ virtual laboratory program (VLP) utilizes PathWave design software to help students develop an understanding of: o the operation of test and measurement (T&M) equipment; o the measurement and analysis of different electrical quantities; and o the selection of T&M equipment Note to Instructors Keysight Technologies’ VLPs are provided as a set of resources to support instructors. Each VLP is comprised of three essential components: o laboratory script(s); o SystemVue workbench(es); and, where needed o configuration file(s) for virtual instruments
Transcript
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Virtual Lab Program: Chapter 4
Digital Modulation Waveforms PathWave System Design (SystemVue)
Introduction Keysight Technologies’ virtual laboratory program (VLP) utilizes PathWave design software to help students develop an understanding of:
o the operation of test and measurement (T&M) equipment; o the measurement and analysis of different electrical quantities; and o the selection of T&M equipment
Note to Instructors Keysight Technologies’ VLPs are provided as a set of resources to support instructors. Each VLP is comprised of three essential components:
o laboratory script(s); o SystemVue workbench(es); and, where needed o configuration file(s) for virtual instruments
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The first component of the VLP, the script (such as this), is self-contained, thus allowing instructors to use it fully (as it stands) or partially (together with other material). Each script is tagged with a set of identifiers that include references to the: level of difficulty; experiment number; stimulus number; objective; and virtual instrument to be used. A summary of these identifiers with cross-references to the scripts and workbenches is given in the instructors’ overview at the end of this section.
The second component of the VLP is a SystemVue workbench. This can be thought of as a signal generator and is arranged in such a way that the student can select predefined signal characteristics using a simple top-level interface. Beneath this, SystemVue code blocks interpret the students’ input selection and correspondingly configure the parameters of schematic components. Upon execution of the simulation, SystemVue generates the required signal which can then analyzed and visualized in the third component of the VLP, the virtual instrument, and/or in SystemVue. In addition to the pre-configured settings, the instructor may adapt the parameter settings in order to provide alternative configurations. The instructor may also choose to adapt the supplied SystemVue workbenches according to their specific requirements and teaching objectives.
Software Versions The workspaces included in this VLP were developed in Keysight PathWave System Design (SystemVue) 2021 and were tested using Keysight PathWave Vector Signal Analysis (89600 VSA) Version 2020. These software packages are recommended as the basis for the VLP.
Instructors’ Overview The SystemVue workspace “Digital modulation waveforms.wsv”—summarized in the table below—has been designed to provide the instructor with a total of 7 x 5 x 3 x 3 x 4 = 1260 experiments.
Parameter Index #1 Index #2 Index #3 Index #4 Index #5 Index #6 Index #7 Index #8
Modulating type BPSK QPSK 8-PSK 16-QAM 32-QAM 64-QAM 128-QAM 256-QAM
Bit streams 20-bit LFSR PN9 PN15 All 0s All 1s - - -
Downloading VLP Packages There are several different VLP packages available for download. To download the various packages, go to www.Keysight.com/find/PathWave-System-Design-Virtual-Labs. This landing page contains links to the PDF lab scripts, workspaces, and configuration files.
Technical and Sales Support PathWave System Design (SystemVue) Technical Support
PathWave System Design (SystemVue) Sales Support
Background for Students In this set of exercises, you will create a variety of signals and visualize them in both the time and frequency domain using Keysight PathWave System Design (SystemVue). A common SystemVue workspace is used for all of the exercises. This is conceptually similar to a laboratory workbench comprised of a signal generator (the source) and signal analyzers (the sinks). The latter includes a time domain data sink which can be thought of as an oscilloscope and a frequency domain sink which is similar to a spectrum analyzer.
To begin with the exercises, it is assumed that you have a PC or laptop on which the suitable software has been installed and that you have access to the relevant workspace which forms part of the VLP.
Prerequisites In order to work through Keysight Technologies’ VLP (either fully or partly), a basic level of competence with SystemVue is required. This should include the ability to:
o open a workspace; o navigate through the workspace tree and view its components; o execute simulations; o adjust workspace parameter settings (mainly by using pre-configured sliders); and
visualize simulation results.
Students who are unfamiliar with any of the above aspects of SystemVue should take advantage of the on-line resources provided in Table 1—a Keysight account might be required.
Table 1. An overview of on-line training resources.
Resource Description On-line link SystemVue video library available
A collection of SystemVue instructional videos presented by Keysight Technologies
https://bit.ly/3cck4vW
Learn SystemVue in 5 mins
A collection of SystemVue instructional videos presented by Anurag Bhargava Tutorial-1: What is Pathwave System Design (SystemVue) Tutorial-2: Understanding SystemVue Design Environment Tutorial-3: Getting Started with Data Flow Simulation in SystemVue Tutorial-4: Working with Graphs in SystemVue Tutorial-8: Vector Modulation Analysis using VSA in SystemVue
Intro to Phased Array Beam Forming and 5GNR Library
workshop covers Phased Array, Beamforming, and 5G NR integration. Data analysis in PathWave VSA is also covered.
Digital Modulation in Communication Systems
Understand concepts of digital modulation and learn new digital modulation techniques in communication systems to make informed decisions to optimize your systems.
Keysight website (5965-7160)
Spectrum Analysis Basics (App Note 150)
Spectrum Analysis Basics teaches the fundamentals of spectrum analyzers and spectrum analysis including the latest advances in spectrum analyzer capabilities.
Keysight website (5952-0292)
Signal Analyzer Fundamentals (What the RF)
This course covers when and how to use different applications and capabilities of signal/spectrum analyzers to make various RF measurements.
Keysight website
Depending on the requirements of your instructor, you might also need to be familiar with how to take screenshots and paste them into a laboratory report. Instructions for doing so in Microsoft Word are available here.
Topics Covered In this VLP, you will experiment with fundamental signal properties including: amplitude; offset; inversion; and frequency. You will investigate sinewaves, square waves and triangular waves in both the time domain and the frequency domain.
Why Digital Communication? Digital communications are a central and indispensable part of today’s society and are used together with wired, wireless or optical networks. To explain why digital is often preferred to analog communications, consider the following two statements concerning digital broadcast radio:
• “Digital radio reception is more resistant to interference and eliminates many imperfections of analog radio transmission and reception. However, there may be some interference to digital radio signals in areas that are far away from a station's transmitter. FM digital radio can provide clear sound comparable in quality to CDs, and AM digital radio can provide sound quality equivalent to that of standard analog FM. FM digital radio also allows broadcasters to offer additional audio channels to the public, using their existing FM frequency.”1
• “The reason digital radio is so reliable is because it employs a smart receiver. Inside each digital radio receiver there is a tiny Computer: a computer capable of sorting through the myriad of reflected and atmospherically distorted transmissions and reconstructing a solid, usable signal for the set to process.”2
Generally speaking, the “tiny computer” mentioned above performs digital signal processing at both the transmitter and the receiver. For transmission, this could include the operations of: encryption; encoding; and modulation. For reception the associated operations are: demodulation; decoding; and decryption.
Wireless Communication and Modulation In simple terms, it could be said that radio frequency, microwave, millimeter-wave and sub-millimeter-wave communication systems all rely on the following fundamental principles:
• an electromagnetic (EM) carrier wave—in essence a sinewave—can transfer energy from a transmitter to a receiver without using wires (hence the term “wireless”); and
• a modulated carrier can be used to transfer information. In other words, by continually altering or modulating the characteristics of a sinusoid, we can use it to transfer information wirelessly.
The purpose of a wireless communication system is, however, not to transfer high frequency energy from a transmitter to a receiver: it is instead to transfer information; the carrier provides the means to do so using high frequency EM waves. These waves (unlike the relatively low frequency information signals) have the ability to travel or propagate through space without cables or wires. All that is needed to form a wireless communication link is an RF transmitter and an RF receiver, each connected to a suitable antenna. The transmitter is an electronic device that places information onto a carrier using a technique called modulation and the receiver is an electronic device that retrieves information form a carrier using demodulation. As the invention of wireless communication dates back to the late nineteenth century, it should be no surprise that many different types of modulation have been developed during since then and indeed continue to be developed to this day.
Digital Modulation In this VL, we shall investigate digital modulation. To do so, we first need to take a step back and look at take a brief look at digital communication before experimenting with the details of digital modulation.
Introduction Digital communication can be defined as the transfer of information that has a discrete or quantized form, both in terms of amplitude and time—in other words, the information being transferred is digital. This can be compared with analog communication in which the information being transferred is analog and continuous, again both in terms of amplitude and time. Digital modulation is thus defined using discrete values or states. These states have two fundamental characteristics: a duration, and a value. Such digital states date back to the earliest form of electrical communication, telegraphy, in which Morse code3 was sent by the operator’s hand using a tool called a key which had two states, “on” and “off”. Using these two values, Morse code symbols are comprised of dots, dashes and spaces, each having a defined duration. The term “keying”, introduced with the telegraph in the 1830s, is still used to this day to describe digital modulation schemes.
Although the difference between analog and digital communication is in the type of the information transferred, all forms of wireless communication rely on a high-frequency electromagnetic carrier wave to propagate or transfer energy (and hence information) from one end of the link to the other. Now since all propagation media are essentially analog in nature (e.g., air, copper cable, glass fiber), the digital data—the bits—need to be converted into an analog signal which can be transmitted. Therefore, within every “digital” communication system there lies an “analog” core.
It can be argued that all communication theory is based on the manipulation of a sinusoidal waveform. For wireless communication—including those that rely on either analog or digital modulation techniques—this is especially true since the solution to Maxwell’s equations for a propagating wave is a sinusoid. In its fundamental form, the signal equation is nearly always written using cosine:
( ) cos( )s t A tω φ= + (1)
3 See for example https://web.northeastern.edu/stemout/morse-code.
Equation (1) identifies the three parameters that are available for modulation of the wireless signal: amplitude A , frequency ω and the phase φ where the units of amplitude, frequency and phase parameters are volts, radians-per-second and radians respectively.
NOTE: In addition to digital modulation, Keysight Technology virtual laboratory scripts and workspaces are also available for basic waveforms, amplitude modulation (AM) waveforms and frequency modulation (FM) waveforms.
State Duration, State Value and State Mapping In contrast to the symbol structure of the Morse code alphabet, nowadays nearly all digital wireless communication signals share a common state duration. On the other hand, state values are taken from a finite set of available signal parameters: amplitude A ; frequency ω ; and phase φ . A digital communication signal is thus comprised of a sequence of individual state values, each of them held constant for the defined state duration. Between each state, a transition occurs.
Depending on the type of modulation used, an analog waveform can represent one or more bits of data. Starting with binary modulation as the simplest form, a +1-bit value is mapped to a first waveform, while a −1-bit value is mapped to a second waveform. The first and second waveforms are each clearly defined and different with respect to each other.
By logical extension, a group of K bits can be used to form a single symbol, which in turn is mapped to one out of a set of 2KM = waveforms: this is known as M-ary modulation, higher order modulation, multilevel modulation or modulation with alphabet size M. Modulation formats differ in the waveforms that are transmitted and in the way that bit groups are mapped to waveforms. Typically, the waveform corresponding to one symbol is time limited to a symbol time Ts and waveforms corresponding to different symbols are transmitted one after the other. The data or bit rate is thus K times the transmitted symbol rate or signaling rate.
A note about time and rates
To avoid confusion, the following definitions should be noted:
• Symbol time (Ts): duration of an information symbol and a signal state. Unit is seconds. • Bit time (Tb): duration of an input binary bit. Unit is seconds. • State duration: duration of a physical signal state, equal to the symbol time. • Symbol rate (fs): reciprocal of the symbol time, equal to the number of signal states
transmitted per second. Unit is baud4. • Bit rate (fb): The number of binary bits transmitted per second. Unit is bits per second. • Baud rate: When commonly used the term “baud rate” is often mistakenly used to mean “bit
rate”, where it more correctly would mean “symbol rate”. This ambiguity must be avoided! Baud is strictly a unit of measure for rate.
4 The unit baud (Bd) is an official SI unit for symbol rate. Baud is named in honor of J. M. Emile Baudot (1845–1903)
who established a five-bits-per-character code for telegraph use which became an international standard (commonly called the Baudot code).
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It should also be noted that bit time is only unambiguous if it refers to a single binary bit stream comprising the input information. It is recommended that digital wireless communication signals are described using symbol time.
• Time (period) and Frequency are often used nearly interchangeably within the technical literature, with sometimes confusing results. While this lax usage is unfortunately tolerated in the literature, within this VLP the use of these terms shall be clear and unambiguous.
Modulation Schemes When choosing the modulation format for a wireless communication system, the goal is to transmit with a certain energy as much information as possible over a channel with a certain bandwidth, while maintaining a certain transmission quality—typically measured as the bit error rate (BER)—given that the channel itself is noisy. This requirement leads to the following criteria:
• The spectral efficiency of the modulation format should be as high as possible. This can best be achieved by a higher order modulation format. This allows the transmission of many data bits with each symbol. However, amongst other things, this comes at the price of two major requirements: high signal-to-noise ratio; and low in-band distortion.
Adjacent channel interference must be small. This entails that the power spectrum of the signal should show a strong roll-off outside the desired band. Furthermore, the signal must be filtered before transmission. This also improves receive sensitivity since noise and interference is rejected. On the downside however, filtering can cause overshoot in the signal trajectory. Typically, this requires more transmission power which could force the amplifier to distort the transmitted signal and thus increase bandwidth. Clearly, a tradeoff is necessary.
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Visualizing Digital Communication Signals In addition to viewing high-frequency signals in the time and frequency domains (using for example an oscilloscope and a spectrum analyzer, respectively), three other graphical tools are in common use: the constellation diagram; the vector diagram; and the eye diagram. These informational diagrams can be used to not only determine how well the digital wireless communication system is operating, but what might be wrong if it is not performing as expected. In the laboratory, these diagrams are available in modern instruments such as the digital sampling oscilloscope (DSO) and the vector signal analyzer (VSA). Each diagram is discussed in the following subsections.
Constellation diagram Constellation diagrams are simply the Cartesian or two-dimensional plots of the signal states from one- or two-dimensional signal state sets. Each state appears as a specific point on this diagram—see Figure 1. The word constellation is borrowed from astronomy, where patterns (constellations) are formed from the stars. The horizontal axis is used for in-phase, or I while the vertical axis is used for quadrature, Q or jQ. Perhaps one of the most important and simplest application of the constellation diagrams is to identify signal modulation – particularly the signal order M.
Figure 1. An example of a constellation plot, in this case for QPSK.
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Vector diagram The vector diagram is essentially a Lissajous pattern, a plot of two separate waveforms on mutually orthogonal axes. Here, the waveforms are the two filtered modulation component waveforms, each plot along its corresponding axis: I or Q. This means that the horizontal points are the successive values of the I waveform component, and the vertical points are the corresponding successive values of the Q waveform component. Both waveforms are scaled by the same factor, so that the entire plot will fit within the unit square. Vector diagrams show what the signal is doing at all times, particularly in between the sampling instants used for the measured constellation diagram—see Figure 2.
It is occasionally valuable to know how fast the signal is traversing along the path in the vector diagram. While the vector diagram itself does not provide this information, it is possible to see if the waveforms in the vector diagram are sampled at some fixed frequency. Then, if the successive points are widely-spaced we know that the circuitry is slewing rapidly under those conditions. Conversely, closely spaced points signify that the signal is moving slowly. Adjacent dot spacing is proportional to the speed of the signal trajectory: wider spacing shows that the signal changes are more rapid.
Constellation plots and vector plots are very often combined as shown for example in Figure 3. Here the four “ideal” constellation points of a QPSK signal representing the are shown in red.
Figure 2. An example of a trajectory plot, in this case for QPSK.
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Figure 3. An example of a combined constellation and trajectory plot, in this case for QPSK, in which the ideal constellation points are shown in red and the signal trajectory between those points is shown in black.
“Eye” diagram The eye diagram is a time domain overlay of multiple waveform components, each waveform section typically having a duration of two symbol times. This allows the full extent of the data waveforms to be visible in the middle of the display. Being fully open in the center of the display, and having the waveform transitions on both the left and right of this opening, the shape of this opening is reminiscent of an eye—see .
Figure 3. An example of an eye diagram, in this case for the in-phase components of a QPSK signal.
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Figure 4. An example of an eye diagram, in this case for the quadrate component of a QPSK signal.
Eye diagrams are extremely useful tools as any errors in modulation magnitude, transition shape, crossover timing and the like are immediately visible on an eye diagram. Most importantly, the eye will “close” if the degradations are severe enough—engineers might discuss how “open the eye is” when discussing system operation. In general, the more “open” the eye is, the more reliable is the operation.
Error vector To introduce the concept of error vector, let us consider just one of these points in which both I and Q are positive as shown in Figure 6—note that the ideal point is now shown in green and the sampled signal is shown in black. Similarly, green is used for the IQ reference vector and black for the IQ measured vector. The error vector is drawn from the end of the IQ reference vector to the end of the IQ measured vector.
Figure 5. A graphical explanation of how the error vector is defined for its various components. The ideal constellation point is denoted by a green-filled circle and the.
I
Q
Q e
rror
I error
IQ phase error
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It should be note that vectors are shown as lines with a single arrowhead whereas measures are shown as lines with a double arrowhead, the latter includes the I error, the Q error, the IQ magnitude error, the IQ phase error and the error vector magnitude (EVM) for sample n, that is to say EVM[n].
In essence, Figure 6 shows a snapshot of the signal at some instance of discrete time associated with a given symbol state. The calculations explained by the figure could therefore be applied to each symbol. Figure 7, Figure 8, and Figure 9 illustrate this for the magnitude error, the phase error and the EVM.
Figure 6. An example of a magnitude error plot, in this case for a QPSK signal.
Figure 7. An example of a phase error plot, in this case for a QPSK signal.
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Figure 8. An example of an EVM plot for a QPSK signal.
Although the ordinate or y-axis of the EVM plot of Figure 9 uses percentage, decibels are often used. Equation (2) shows the general relationship between signal-to-noise ratio (SNR) and EVM in which the peak-to-average power ratio (PAPR) is specific to the particular modulation scheme:
10[%][dB] [dB] 20log
100EVMSNR PAPR = − +
(2)
As EVM is a ratio of voltages, 1020 log is used to return a power ratio. The minus sign which appears
outside the square brackets is necessary because SNR is a ratio of signal to noise whereas EVM is a ratio of noise to signal.
Other plot types In addition to the aforementioned plots, signals can also be displayed with spectrograms (spectrum vs. frequency vs. time). Furthermore, signal statistics can be plotted as a probability distribution function (PDF), cumulative distribution function (CDF) of a complementary CDF (CCDF).
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Summary In this section, we briefly reviewed digital communications and discussed some of the most important aspects of digital modulation. We also explored some of the methods used to visualize and characterize digitally modulated signals.
Overview Level 2 Experiment reference number 04 Stimulus reference number 001-1260 Objective number 2 (Digital modulation waveforms, simulation and analysis) Instrument SystemVue, VSA
Learning Objective In this Virtual Laboratory (VL), students will use Keysight PathWave System Design (SystemVue) electronic system-level design software to explore and measure signals. This VL will assist students in their understanding of signal analysis with the following learning objective(s):
o Observe a signal in the time domain and identify its: amplitude; peak voltage; and peak-to-peak voltage.
o Observe a signal in the frequency domain and identify its amplitude, frequency and bandwidth.
o Observe a signal in the signal domain and: compare its trajectory against a given constellation; study its “eye” diagrams for I and Q; and measure its error vector magnitude.
Student Outcomes Upon successful completion of this VL exercise, students will:
o Be familiar with the principle of the VLP. o Understand how to execute a SystemVue simulation, change parameter settings and
collect data. o Analyze and measure signals in the time, frequency and signal domains using both
SystemVue and VSA. o Interpret spectral plots and eye diagrams. o Understand the basics of digital modulation and identify how signal and modulation
parameters affect the resulting waveforms in the time, frequency and signal domains.
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Procedure The following steps will help you through the procedure needed to complete a successful simulation and to then visualize and analyze the resulting simulation data. In this VL, you will create simple waveforms, adjust the values of certain parameters that describe the waveforms and produce graphs or plots of the waveforms in both the time and frequency domains.
Step 1: Starting SytemVue and opening the workspace 1. Start SystemVue on your computer using any of the following methods:
a. From the Windows start menu navigate to SystemVue 2021 SystemVue 2021.
b. Tap the Windows key and then start typing “Syst…” until SystemVue appears. Select it with the mouse or cursor and press enter; or
c. Double click on the desktop icon which was placed there during the installation of SystemVue (see Figure 10)
Figure 10. The SystemVue 2021 icon is normally placed on the desktop when the software is installed.
2. After SystemVue has loaded, you will probably be greeted with a “Getting Started with SystemVue” screen, similar to that shown in Figure 11.
Figure 11. The "Getting Started with SystemVue" screen normally appears just after the program is started.
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3. In the top panel, click on More Workspaces and using the file explorer, navigate your way to the workspace “Digital modulation waveforms.wsv”. This workspace (and perhaps others too) might have already been installed on the machine you are using or on a network drive to which you have access. It is recommended that you save a local copy of the workspace and use that version to work with. This will allow you to revert to the original version with its default settings should the need arise.
Step 2: Understanding the SystemVue window 1. After you have successfully opened the workspace, your screen should be similar to that shown in
Figure 12.
Figure 12. The default view of the “Digital Modulation Waveforms” workspace in SystemVue.
2. The default view of the FM Waveforms workspace comprises a number of panels or windows. These are listed below together with links to the relevant parts of the user manual:
a) The workspace tree – see: Home > Users Guide > Environment > Design Environment > Workspace Tree SystemVue 2021: qthelp://systemvue.2021/doc/users/Workspace_Tree.html
b) The design – see: Home > Users Guide > Using PathWave System Design > Designs SystemVue 2021: qthelp://systemvue.2021/doc/users/Designs.html
c) A graph (for time domain analysis) – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Graphs.html
d) A graph (for frequency domain analysis) – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Graphs.html
4. The design window shows an apparently very simple schematic diagram which has been arranged into three main areas:
a) A signal source which is configured using predefined parameter values selectable thru the use of sliders. In this step and the next, it is recommended to leave the sliders set to their default positions. The source parameters are grouped into five sets:
i. Modulation Type Selection – this slider allows the student to select one of the following modulation types: 'BPSK' (1); 'QPSK' (2); '8-PSK' (3); '16-QAM' (4); '32-QAM' (5); '64-QAM' (6); '128-QAM' (7); and '256-QAM' (8).
ii. Bit Stream Selection – this slider allows the student to select one of the following bit streams: '20-bit LFSR' (1); 'PN9' (2); 'PN15' (3); 'All 0s' (4); and 'All 1s' (5).
iii. Symbol Rate Selection – this slider allows the student to select one of the following symbol rates: 1e6 Bd (1); and 3e6 Bd (2).
iv. Carrier Frequency Selection – this slider allows the student to select one of the following carrier frequencies: 750 MHz (1); 2.0 GHz (2); 28.5 GHz (3); and 48.25 GHz (4).
v. Carrier Power Selection – this slider allows the student to select one of the following carrier powers: -80 dBm (1); 0 dBm (2); 30 dBm (3); and 36 dBm (4).
b) An area showing three different sinks. These are used in SystemVue to collect data during a data flow simulation. In this step and the next, it is recommended to leave the sliders set to their default positions. The sinks shown are:
i. TimeSink, this is used to visualize and analyze the signal in the time domain. By default, the sink is activated (1). It can be controlled using the slider useTimeSink – see: Home > Part Catalog > Algorithm Design Library > Sinks Category > Sink Part > Sink (Data Sink) SystemVue 2021: qthelp://systemvue.2021/doc/algorithm/Sink.html
ii. SpectrumSink, this is used to visualize and analyze the signal in the frequency domain. By default, the sink is activated (1). It can be controlled using the slider useSpectrumSink – see: Home > Part Catalog > Algorithm Design Library > Sinks Category > SpectrumAnalyzer Part SystemVue 2021: qthelp://systemvue.2021/doc/algorithm/SpectrumAnalyzer_Part.html
iii. SvDemodSink, this is used to visualize and analyze the signal in the signal domain. By default, the sink is activated (1). It can be controlled using the slider useSvDemodSink – see: Home > Part Catalog > Algorithm Design Library > Sinks Category > DigitalDemod Part SystemVue 2021: qthelp://systemvue.2021/doc/algorithm/DigitalDemodCx.html
iv. VSA, this is used to visualize and analyze the signal in the signal domain. By default, the sink is deactivated (0). It can be controlled using the slider useVSA – see Home > Part Catalog > Algorithm Design Library > Instrumentation Category > VSA 89600B Sink Part SystemVue 2021: qthelp://systemvue.2021/doc/algorithm/VSA_89600B_Sink.html
c) An area that presents a textual summary of the parameter settings used for: the modulating signal showing the type of waveform, whether or not it is inverted, its frequency and its amplitude; the modulation index; and the amplitude of the carrier.
Step 3: Executing the simulation with default parameter settings 1. Using the default settings for both the source parameter values and the sink activation controls (see
Figure 13), execute the simulation by using anyone of the following methods:
a) Click on the green Run Analyses arrow shown below:
Figure 14. A closeup view of the menu bar and main toolbar showing the green Run Analyses button.
b) On the menu bar, go to Action -> Run All Out-of-Date Analyses and Sweeps; or
2. A status display window similar to that shown below will appear on your screen and, since the digital demodulation sink is activated by default, SystemVue will run continuously until the stop button is clicked—let the data flow simulation run.
Figure 15. The SystemVue data flow simulation status window appears during the execution of a simulation. (When you reach Step 3.4, use the stop button to terminate the simulation.)
3. SystemVue will also open a dynamic graph display window, similar to that shown below. This is used to visualize and analyze the signal in the signal domain—the example shows the combined constellation and trajectory plot; the I-eye and Q-eye diagrams; and a collection of plots and a table relating to EVM.
Figure 9. The SystemVue digital demodulation window appears during the execution of a simulation.
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4. Once you are familiar with the digital demodulation plots and are ready to stop the simulation, simply click on the “stop” button (see Figure 15). A successful simulation will result in a status display window which is free of errors and warnings as shown in Figure 17.
Figure 10. A successful SystemVue simulation results in an error- and warning-free status window.
Step 4: Post-simulation visualization and analysis 1. The Digital modulation waveforms workspace includes two graph windows. These were shown as
‘c’ and ‘d’ in Figure 12 before the simulation was executed and were thus labelled “No Data”.
2. Now that the system has simulated successfully, the two graph windows should resemble Figure 18 for the time domain and Figure 19 for the frequency domain.
Figure 11. A SystemVue graph window showing the instantaneous signal voltage plotted against time [ms]. The left Y-axis shows the modulating signal while the right Y-axis shows the modulated carrier.
I [V]
Q [V
]
-20
-12
-4
4
12
20
I [V]-20 -12 -4 4 12 20
Constellation Plot
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Figure 19. A SystemVue graph window showing the signal waveform in the frequency domain in which the signal power (developed in a 50 ohm resistor) [dBm] is plotted against frequency [kHz].
3. SystemVue graphs enable you to explore and examine your data in many different ways. The user manual provides detailed instructions that include:
a) An overview – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Graphs.html
b) Zooming a graph – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs > Zooming Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Zooming_Graphs.html
c) Using markers on graphs – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs > Using Markers on Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Using_Markers_on_Graphs.html
d) Annotate a graph – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs > Annotating Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Annotating_Graphs.html
e) Copying and saving a graph – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs > Copying and Saving Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Creating_Graphs.html#CreatingGraphs-CopyingandSavingGraphs
f) Creating a graph – see: Home > Users Guide > Using PathWave System Design (SystemVue) > Graphs > Creating Graphs SystemVue 2021: qthelp://systemvue.2021/doc/users/Creating_Graphs.html
Step 5: Activate the VSA sink 1. Using the default settings for both the source parameter values and the sink activation controls,
change the useVSA slider to activate the VSA sink as shown in Figure 20. Execute the simulation by using anyone of the following methods described in Step 2.1.
Figure 20. The “Digital modulation waveforms” design window showing source, sink and waveform settings.
2. If VSA is correctly installed on your computer, you should see a stimulus status window similar to that shown in Figure 21. Please note (as explained in the status window) that it may take a couple of minutes for VSA to start.
Figure 12. The SystemVue data flow simulation status window appears during the execution of a simulation and in this example shows that VSA is initializing.
3. After a couple of minutes, VSA will open in a new window, separately to SystemVue. VSA is a software program that runs on your computer. However, although the software is running on your computer and working with a virtual signal created by SystemVue, the very same program can also be integrated into Keysight instrumentation that is used to perform measurements of radio signals in the laboratory. In other words, it uses exactly the same signal processing techniques to analyze and visualize signals whether they be virtual or physical. In order to help you get started with VSA, a configuration file5 is automatically sent to VSA according to the modulation type selected in SystemVue. Since the default modulation type is QPSK, the VSA software should present you with a window similar to that shown in Figure 22.
Figure 22. An example of the VSA display window, in this case for a QPSK signal.
5 The contents of the ZIP archive—including both the workspace and the VSA configurations—should be extracted to
the same folder.
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4. With help from your instructor and the VSA resources detailed in Table 1, explore VSA.
5. Once you are familiar with the digital demodulation plots in VSA and are ready to stop the simulation, simply click on the “stop” button (see Figure 15). A successful simulation will result in a status display window which is free of errors and warnings as shown in Figure 17.
Step 6: Explore parameter settings 1. Now that you have completed your first simulation and have viewed and analyzed the results
obtained, you should be ready to investigate what happens when other modulation parameter settings are used.
2. Your instructor might provide you with a list of configuration settings to explore. If not, you are encouraged to make small changes to the settings, re-simulate and observe the changes. For example, now that you have analyzed the default settings, you might like to visualize what happens when you:
a) Change the type of modulation; b) Change the bit stream; c) Change the symbol rate; d) Change the carrier frequency; and e) Adjust the power of the carrier.
3. Referring to the section “Topics covered”, you should make sure that you understand the relationship of ‘a’ to ‘e’ above and their effect on the modulated signal. In addition, you should also be familiar with:
a) Measuring signal quantities from plots and calculating the frequency of a periodic signal from an estimation of its period in the time domain.
b) Using graph markers. c) The relationship between signal amplitude and signal power. d) Decibels and the unit dBm. e) The fundamentals of digital modulation. f) The different ways of visualizing a signal. g) A basic understanding of digital communications.
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Review Congratulations, you have now completed your first virtual laboratory and have:
o Observed a signal in the time domain and identified its: amplitude; peak voltage; and peak-to-peak voltage.
o Observed a signal in the frequency domain and identified its amplitude, frequency and bandwidth.
o Observed a signal in the signal domain and: compared its trajectory against a given constellation; studied its “eye” diagrams for I and Q; and measured its error vector magnitude.
o Become familiar with the principle of the VLP. o Understood how to execute a SystemVue simulation, change parameter settings and
collect data. o Analyzed and measured signals in the time, frequency and signal domains using both
SystemVue and VSA. o Interpreted spectral plots and eye diagrams. o Understood the basics of digital modulation and identied how signal and modulation
parameters affect the resulting waveforms in the time, frequency and signal domains.
Suggested Exercises In addition to the tasks assigned to you by your instructor, here are some exercises that you might like to try:
1. Using the modulation type selector and any pseudo random bitstream, visualize the signal produced in the time, frequency and signal domains.
2. Using QPSK modulation and any pseudo random bitstream, vary the symbol rate and describe which signal characteristics are affected.
3. Using QPSK modulation and the lowest symbol rate, set the bitstream to “All 0s” (i.e., a non-pseudo random pattern) and explain the resulting constellation and trajectory plots.
4. Repeat exercise 3 using “All 1s” and explain the results.
5. Using settings similar to those used in exercise 2, change the carrier frequency and explain the resulting waveforms produced.
6. Using settings similar to those used in exercise 2, change the carrier ampitude and explain the resulting waveforms produced.
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7. Determine the modulation scheme of your favorite technology standard (e.g., 5G NR). Simulate this waveform in the SystemVue workspace and activate the VSA sink.
a. Using VSA to perform the advanced signal demodulation of your waveform, comment on the: “eye diagrams”; the EVM; and the occupied bandwidth.
b. Using the support documentation provided with the software, explore some the various types of plots that are available in VSA.
c. Use VSA to measure, calculate and visualize the CDF of your signal and determine the PAPR (refer to the introductory notes).
Acknowledgement Keysight would like to thank Dr. Paul Leather at Technische Hochschule Rosenheim for his help in developing these lab guides.
