Hands on with the NI USRP

Hands on with the NI USRP
UNE INTRODUCTION À LA
RADIO DÉFINIE PAR LOGICIEL
avec NI LabVIEW et NI USRP
Version 1.1 – Q4 2013
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Contents
Overview .......................................................................................................................................... 1
Purpose of the Hands-on Seminar ............................................................................................... 1
What You Will Do......................................................................................................................... 1
Why You Should Take This Course .............................................................................................. 1
Time Required to Complete Course ............................................................................................. 1
Required Background................................................................................................................... 1
Required Equipment ......................................................................................................................... 2
Hardware ..................................................................................................................................... 2
Software ...................................................................................................................................... 2
Configuring Hardware .................................................................................................................. 2
Software Defined Radio Fundamentals .............................................................................................. 4
What is Software Defined Radio? ................................................................................................ 4
Digital Communication System Fundamentals ............................................................................. 5
USRP Hardware ........................................................................................................................... 6
What is a Computer’s Role in SDR? ............................................................................................. 7
Finding Hardware & Installing Software ............................................................................................. 8
Identifying the Right Hardware .................................................................................................... 8
Finding the Specifications Online ................................................................................................. 8
NI USRP Online Community ........................................................................................................ 8
Purchasing Hardware ................................................................................................................. 10
Installing Software ..................................................................................................................... 10
Development Environment: NI LabVIEW ............................................................................ 10
Hardware Driver: NI-USRP .................................................................................................. 10
Academic Site License ....................................................................................................... 10
NI-USRP LabVIEW Driver ................................................................................................................ 11
NI-USRP Example Programs ...................................................................................................... 11
NI-USRP Help Files .................................................................................................................... 11
NI-USRP Functions Palette ........................................................................................................ 12
niUSRP Property Node ............................................................................................................... 13
The Eight Most-Used NI-USRP Functions .................................................................................. 13
Configure Functions............................................................................................................ 14
Read/Write Functions ......................................................................................................... 16
Close Functions .................................................................................................................. 18
USRP Receive and Transmit Examples ............................................................................................ 19
Single Channel, Finite ................................................................................................................ 19
Single Channel, Continuous ....................................................................................................... 20
Multiple Channel, Continuous .................................................................................................... 21
Avant de commencer : l'environnement LabVIEW ..................................................................... 22
Préparer LabVIEW........................................................................................................................... 23
Raccourcis LabVIEW .................................................................................................................. 27
Travaux Pratiques ........................................................................................................................... 29
Exercice1 : Trouver une station radio ......................................................................................... 31
Exercice 2 : Démoduler une radio FM ........................................................................................ 35
Explication sur le flux de données ....................................................................................... 38
Explication sur l'algorithme ................................................................................................. 39
Exercice 3 : communications numériques.................................................................................. 47
On Your Own Exercise 4: LabVIEW Tips and Tricks ................................................................... 49
Tools Palette ....................................................................................................................... 49
Automatically Wiring Objects .............................................................................................. 50
LabVIEW Graphs vs. Charts ................................................................................................ 51
Customizing Graphs............................................................................................................ 52
Working with Graphs .......................................................................................................... 52
Additional Training .......................................................................................................................... 55
Self-Paced Video Training for Students ...................................................................................... 55
Professional Training Options .................................................................................................... 56
NI Certification Path ................................................................................................................... 56
Appendix A: Exercise Solution Screenshots ..................................................................................... 57
Exercise 1 .................................................................................................................................. 57
Exercise 2 A ............................................................................................................................... 58
Exercise 2 B ............................................................................................................................... 59
Exercise 2 C ............................................................................................................................... 60
Exercise 3 .................................................................................................................................. 61
Exercise 4 .................................................................................................................................. 61
Glossary A: RF & Communication Reference ................................................................................... 63
Overview
Purpose of the Hands-on Seminar
This hands-on seminar seeks to educate researchers and graduate students in the fields of science and
engineering on the fundamental concepts of wireless signal acquisition. You will physically setup and
plug in a USRP, write a program in LabVIEW, and then visualize the results.
The exercises are examples of how to acquire, analyze, and present data for applications involving
wireless signals. While the exercise is generic, we hope that you can apply what you learn to your own
applications. For future reference, this manual is available both electronically and in print.
What You Will Do
Through three main exercises that contain sub-sections, you will use LabVIEW and the NI USRP 2920
to create a FM radio receiver. There are also supplementary exercises that teach you how to create a
custom LabVIEW user interface, how to configure the USRP, and a glossary for the common terms
used in this document.
The presenter will start with a quick presentation that defines some common terms and describes
how National Instruments hardware and software approach the task.
Why You Should Take This Course
You should take this course if you:
- are researching wireless communications
- need to quickly and easily prototype and validate algorithms
- looking to evaluate the usefulness of software defined radio in your research
- need exposure to setting up software defined radio
Time Required to Complete Course
The course should take approximately three hours, but this time can vary depending on your
background.
Required Background
It is recommended that you have some exposure to LabVIEW, but it is not required. The instructions
for the exercises will cover all necessary steps to complete the task. It should be noted that you will be
expected to learn basic tasks as you progress, and the instructions will become less detailed and
require that you retain some of the knowledge. Visit ni.com/academic/students/learn-labview to learn
more.
You will be expected to be familiar with using a computer, a mouse, a keyboard, and basic wireless
communication concepts.
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Required Equipment
Hardware





NI USRP-2920 device
NI USRP universal power adapter
Gigabit (Gb) Ethernet cable
Antenna
Computer with a spare Gigabit (Gb) Ethernet port
Software




NI LabVIEW 2012 or later
NI USRP 1.1 or later
NI Modulation Toolkit
LabVIEW MathScriptRT Add On
Configuring Hardware
The following steps are an overview of the NI USRP-292x Getting Started Guide. Follow these steps
after you install LabVIEW on your computer:
1. Install the NI USRP Software Suite DVD. The software suite adds the following items to your
LabVIEW installation: the NI-USRP driver, LabVIEW Modulation Toolkit, LabVIEW MathScriptRT
module, and LabVIEW Digital Filter Design Toolkit. For more information, refer to the Installing
the Software section of this document.
2. Referring to Figure 1, attach the antenna to the front of the NI USRP-292x.
3. Connect the device directly to your computer with the enclosed Ethernet cable and plug in the
power. For more information, refer to the Installing and Configuring the Hardware section of
this document.
4. Change the IP address of your computer’s Ethernet port to a static IP. NI recommends a static
IP address of 192.168.10.1 because NI USRP-2920 has a default IP address of 192.168.10.2.
For more information, refer to the Installing and Configuring the Hardware section (page 8).
5. Examples are located in LabVIEW. Navigate to the start menu and select Start » All Programs »
National Instruments » NI-USRP » Examples. For more information, refer to the Programming
the NI 292x section of this document on page 11.
6. If you have trouble with any of these steps, refer to the Appendix of this document or watch
the video at ni.com/usrp/gettingstarted
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Install antenna on
RX1 TX1 port
Connect Gb Ethernet
cable to a host PC
Connect power
Figure 1. USRP Front Panel
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Software Defined Radio Fundamentals
This section reviews the fundamental concepts of software defined radio.
What is Software Defined Radio?
The Wireless Innovation Forum defines Software Defined Radio (SDR) as:
“Radio in which some or all of the physical layer functions are software defined.” 1
SDR refers to the technology wherein software modules running on a generic hardware platform are
used to implement radio functions. Combine the NI USRP hardware with LabVIEW software for the
flexibility and functionality to deliver a platform for rapid prototyping involving physical layer design,
wireless signal record & playback, signal intelligence, algorithm validation, and more.
Figure 2. Simplified Overview of a SDR Setup Built Around an NI USRP
1
http://www.sdrforum.org/pages/documentLibrary/documents/SDRF-06-R-0011-V1_0_0.pdf
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Digital Communication System Fundamentals
A typical digital communication system includes a transmitter, a receiver, and a communication
channel. Figure 3 illustrates the general components of a digital communication system. The
transmitter, shown as blocks on the top row, contains blocks for source and channel coding,
modulation, simulating real-world signal impairments, and up conversion. The receiver, which includes
the blocks in the bottom row, has blocks for down conversion, matched filtering, equalization,
demodulation, channel decoding and source decoding. Refer to the NI LabVIEW Modulation Toolkit
online Help for more information about measurement and visualization tools for digital communication
systems.
Figure 3. Digital Communication System Block Diagram
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USRP Hardware
The NI USRP connects to a host PC to act as a software-defined radio. Incoming signals attached to
the standard SMA connector are mixed down using a direct-conversion receiver (DCR) to baseband I/Q
components, which are sampled by a 2-channel, 100 MS/s, 14-bit analog-to-digital converter (ADC).
The digitized I/Q data follows parallel paths through a digital downconversion (DDC) process that
mixes, filters, and decimates the input 100 MS/s signal to a user-specified rate. The downconverted
samples, when represented as 32-bit numbers (16 bits each for I and Q), are passed to the host
computer at up to 20 MS/s over a standard Gigabit Ethernet connection.
For transmission, baseband I/Q signal samples are synthesized by the host computer and fed to the
USRP-2920 at up to 20 MS/s over Gigabit Ethernet when represented with 32-bits (16-bits each for the
I and Q components). The USRP hardware interpolates the incoming signal to 400 MS/s using a digital
upconversion (DUC) process and then converts the signal to analog with a dual-channel, 16-bit digitalto-analog converter (DAC). The resulting analog signal is then mixed up to the specified carrier
frequency.
An available 8-bit mode, in which 16-bits total are used to represent the I and Q values of a
downconverted sample or sample to be upconverted, can enable a transfer rate of up to 40 MS/s over
the Gigabit Ethernet connection between the host PC and the USRP.
TX
RX
Analog RF Transceiver
Fixed Function FPGA
PC
Figure 4. USRP Block Diagram
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What is a Computer’s Role in SDR?
A software-defined radio system is a radio communication system in which certain
hardware components are implemented in software. These hardware components
include filters, amplifiers, modulators, and demodulators. Because these
components are defined in software, you can adjust a software-defined radio system
as needed without making significant hardware changes. Since computers today
may contain very fast processors and high-speed interfaces, we can leverage these abilities for our
software defined radio by implementing them on a computer quickly, using LabVIEW.
Driver Software
Driver software provides application software the ability to interact with a device. It simplifies
communication with the device by abstracting low-level hardware commands and register-level
programming. Typically, driver software exposes an application programming interface (API) that is
used within a programming environment to build application software.
For the USRP, NI-USRP is the hardware driver. As mentioned below, NI offers development
environments that can make driver calls into NI-USRP, but other text-based environments can also
access the hardware driver.
Application Software
Application software facilitates the interaction between the computer and user for acquiring, analyzing,
processing, and presenting measurement data. It is either a prebuilt application with predefined
functionality, or a programming environment for building applications with custom functionality.
Custom applications are often used to automate multiple functions of a device, perform signalprocessing algorithms, and display custom user interfaces.
The NI-USRP driver currently supports the National Instruments’ LabVIEW graphical development
environment software for rapidly developing custom applications.
For more information, navigate to ni.com and search for “Out-of-the-Box Video with NI USRP.” If you
are viewing this digitally, click here to access this Developer Zone tutorial directly.
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Finding Hardware & Installing Software
It is first important to understand the complexities and requirements of your application to ensure that
your wireless signal system is the right fit.
Identifying the Right Hardware
To help you identify the right hardware for your system, first navigate to ni.com/usrp. At this portal you
will find everything that you need to know about the USRP. You can use the left-hand navigation facets
to begin your search and narrow in on the right selection.
Finding the Specifications Online
The most important document for any device is the specifications document. This document is housed
on the product page for each device. Once you know the device of interest, it is easiest to find the
device using the search box in the upper right hand corner of the ni.com website. Simply enter the
product model number (i.e., 2920) and click search. An example search query is shown on the next
page, with the product page result outlined in red.
NI USRP Online Community
This ni.com community is the home for example VIs associated with the NI USRP, "Universal Software
Radio Peripheral." Browse to find a starting point, or post your own NI-USRP-based examples.
Navigate to ni.com/usrp and click the Code Sharing Community image.
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Glossary A: RF & Communication Reference for help understanding any terms in the Specifications
Documents
Figure 5. Search Results for “2920” at ni.com
Once on the product page, click on the Resources tab to surface documents about the device; you can
also access the complete NI USRP Specifications document for the device by clicking on the Manuals
link.
Figure 6. Product Page for NI USRP-2920
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Purchasing Hardware
To receive a quote for NI USRP Hardware, you can add the hardware to your cart at ni.com from the
product page for the product. You can also call your NI Sales Engineer to help design the best system
for your application.
To speak with a technical representative, navigate to ni.com and click on the Contact Us link on the
homepage.
Installing Software
To acquire data from the USRP, you will need to first install a software development environment and
then the hardware driver.
Development Environment: NI LabVIEW
The development environment facilitates the interaction between the computer and user for acquiring,
processing, analyzing, and presenting measurement data. It is either a prebuilt application with
predefined functionality, or a programming environment for building applications with custom
functionality. Custom applications are often used to automate multiple functions of a device, perform
signal-processing algorithms, and display custom user interfaces.
The primary development environment for NI-USRP is NI LabVIEW. LabVIEW is a graphical
programming language that abstracts the low-level complexities of text-based programming into a
visual language that scientists and engineers use worldwide to acquire, analyze, process, and present
data in the same environment.
Visit ni.com/trylabview for more information and to download an evaluation.
Hardware Driver: NI-USRP
Driver software provides application software the ability to interact with a device. It simplifies
communication with the device by abstracting low-level hardware commands and register-level
programming. Typically, driver software exposes an application-programming interface (API) that is
used within a programming environment to build application software.
The hardware driver for the USRP is NI-USRP. The USRP driver comes with example LabVIEW
programs and help files to get you started.
Visit ni.com/drivers and search for ‘USRP’ to download the latest version of the driver.
Academic Site License
If you are on a university with access to an Academic Site License (ASL), then you might have free
access to almost all NI software, including LabVIEW. Contact your university software administrator for
more information.
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NI-USRP LabVIEW Driver
When installed the NI USRP hardware driver automatically installs example programs, help files, and
functions.
NI-USRP Example Programs
To locate example files for using the USRP driver in LabVIEW, navigate to the Start Menu » All
Programs » National Instruments » NI-USRP » Examples.
NI-USRP Help Files
There are two forms of help offered within the LabVIEW development environment: Context Help and
Detailed Help.
Context Help
The context help window displays basic information about LabVIEW objects when you move the
cursor over each object. To toggle the display of the context help window, select Help » Show Context
Help or press <Ctrl-H>.
When you move the cursor over front panel and block diagram objects, the context help window
displays the icon for subVIs, functions, constants, controls, and indicators, with wires attached to each
terminal. When you move the cursor over dialog box options, the context help window displays
descriptions of those options.
Figure 7. LabVIEW Context Help
If a corresponding detailed help topic exists for an object that the context help window describes, a
blue detailed help link appears in the context help window (Figure 7). Click the link or the button to
display the LabVIEW help for more information about the object.
Detailed Help (LabVIEW Help)
The LabVIEW help is the best source of detailed information about specific features and functions in
LabVIEW. Detailed help entries break down topics into a concepts section with detailed descriptions
and a how-to section with step-by-step instructions for using LabVIEW functions.
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You can access the LabVIEW Help by selecting Help » Search the LabVIEW Help, or clicking the blue
Detailed help link in the context help window. You also can right-click an object and select Help from
the shortcut menu.
Figure 8. Detailed LabVIEW Help
NI-USRP Functions Palette
To access the NI-USRP functions in LabVIEW, navigate to the block diagram and right-click empty
white space to bring up the functions palette. Then navigate to Instrument Drivers » NI-USRP. The
functions will appear similar to the palette below. Drag and drop a function onto the block diagram to
begin programming.
Figure 9. NI-USRP Palette in LabVIEW
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niUSRP Property Node
Use the niUSRP properties to access advanced configuration options for NI-USRP driver applications.
Figure 10. niUSRP Property Node
The Eight Most-Used NI-USRP Functions
The following section outlines the eight most-used USRP functions to help get you started with your
experiments. They have been grouped in categories by their functionality. These categories are:
Configure, Read/Write, and Close. These categories are included in most data acquisition programs
and are important programming models to consider when creating a new LabVIEW Virtual Instrument
(VI).
Figure 11. The Eight Most-Used NI-USRP Functions
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Configure Functions
niUSRP Open Rx Session
The niUSRP Open Rx Session VI is the first VI that is used to create a software session with
the USRP for receiving an RF signal. A session is necessary to send configuration data and
retrieve IQ data from the USRP.
An Rx session can only be used with Rx functions.
Figure 12. Context Help for niUSRP Open Rx Session VI
niUSRP Configure Signal
The niUSRP Configure Signal VI can be used with a receive (Rx) or a transmit (Tx) session. It
sets the IQ rate, carrier frequency, gain, and active antenna. For multiple USRP configurations
the channel list specifies a specific USRP. Not all IQ rates, frequencies and gains are valid. Always read
the coerced values to see if the requested and actual (coerced) values are different.
Figure 13. Context Help for niUSRP Configure Signal VI
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niUSRP Initiate
The niUSRP Initiate VI starts the receive session and tells the USRP that all configuration is
complete and that the USRP should begin to capture IQ data (samples).
This VI can only be used with an Rx session.
Figure 14. Context Help for niUSRP Initiate VI
niUSRP Open Tx Session
The niUSRP Open Tx Session VI is the first VI that is used to create a connection to the USRP
for transmitting an RF signal. A session is necessary to send configuration data and send IQ
data to the USRP.
A Tx session can only be used with Tx functions.
Figure 15. Context Help for niUSRP Open Tx Session VI
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Read/Write Functions
niUSRP Fetch Rx Data (Polymorphic)
The niUSRP Fetch Rx Data VI allows you to retrieve IQ data from a USRP that has an Rx
session created with the niUSRP Open Rx Session VI. This data can then be graphed in
time domain, or digitally processed for analysis.
This VI is polymorphic, meaning that there are several versions (instances) of the VI available to choose
from depending on the data type you wish to work with.
This VI can only be used with an Rx session.
Figure 16. Context Help for niUSRP Fetch Rx Data VI
niUSRP Write Tx Data (Polymorphic)
The niUSRP Write Tx Data VI allows you to send IQ data to the USRP so that it may
transmit that data at the carrier frequency specified by the niUSRP Configure Signal VI.
This VI is polymorphic, meaning that there are several versions (instances) of the VI available to choose
from depending on the data type you wish to work with.
This VI can only be used with a Tx session.
Figure 17. Context Help for niUSRP Write Tx Data VI
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NI-USRP Read and Write Data Types
There are several instances of Write Tx Data and Fetch Rx Data VIs to choose from for your
convenience. The table below represents the options available instances.
Polymorphic Type
Description
Complex Double Cluster
Fetches a cluster of complex, double-precision floating-point
data from the specified channel. Modulation Toolkit VIs use the
complex, double-precision floating-point cluster data type. Use
this VI in applications that use Modulation Toolkit VIs.
Complex Double Waveform Data
Fetches complex, double-precision floating-point data in a
waveform data type from the specified channel.
Complex Double
Fetches complex, double-precision floating-point data from the
specified channel.
16-bit Integer
Fetches complex, 16-bit signed integer data from the specified
channel. To use this VI, you must set the Host Data Type
property to I16.
2D Array Complex Double
Fetches complex, double-precision floating-point data from
multiple channels.
2D Array 16-bit Integer
Fetches complex, 16-bit signed integer data from multiple
channels. To use this VI, you must set the Host Data Type
property to I16.
Table 1. NI USRP Read and Write Data Types
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Close Functions
niUSRP Abort
The niUSRP Abort VI tells the USRP to stop an acquisition in progress. This VI allows you to
change configuration settings without completely closing the session and creating a new
session.
This VI can only be used with an Rx session.
Figure 18. Context Help for niUSRP Abort VI
niUSRP Close Session
The niUSRP Close Session VI closes the current Rx or Tx session and releases the memory in
use by that session. After calling this VI you can no longer transmit to or receive data from the
USRP until you re-open a new session.
Figure 19. Context Help for niUSRP Close Session VI
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USRP Receive and Transmit Examples
The following examples are the skeleton programs for transmitting and receiving. Each example will
have a few example applications, along with example LabVIEW block diagram code to help get you
started. These examples can be found at Start » All Program » National Instruments » NI USRP »
Examples
Single Channel, Finite
Applications: Burst data transmits, frequency hopping, large frequency sweeps
Example VI Name: niUSRP EX One Shot Rx.vi
The following table lists out the VIs that you will use for this type of application. Note that some VIs are
required, others can be added for more advanced functionality and some are not applicable.
NI-USRP VI
Open Session
Configure Signal
Initiate
Fetch/Write Data
While Loop
USRP Property Node
Abort
Close Session
Acquire




Transmit








The single channel finite example can be used as a starting point for a simple transmitter that transmits
bursts of data. A while loop is not needed if only a single burst of data needs to be transmitted. Using
a while loop and the abort and initiate VIs we can change the frequency of the carrier frequency on the
fly without closing and reopening Rx sessions (which takes extra time). For finite Tx sessions, a
boolean indicator called End of Data? is set to true to let the USRP turn off the transmitter after the last
sample has been transmitted.
Figure 20. Example block diagram code for single USRP (channel) finite acquisition
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Single Channel, Continuous
Application: Burst data reception, power lever monitoring, continuous transmission
Example VI Name: niUSRP EX Rx Continuous Async.vi
The following table lists out the VIs that you will use for this type of application. Note that some VIs are
required, others can be added for more advanced functionality and some are not applicable.
NI-USRP VI
Open Session
Configure Signal
Initiate
Fetch/Write Data
While Loop
USRP Property Node
Abort
Close Session
Acquire








Transmit






The single channel continuous example is almost identical to the finite example except the added
while loop. This is useful to keep from missing a transmission that comes in bursts or to receive a
transmission that is continuous. For Rx sessions, the abort and initiate VIs are not used inside the
while loop, which keeps the transmitter on continuously. For Tx sessions, the End of Data? boolean
indicator is set to false to keep the transmitter on continuously. If your loop does not fetch or write fast
enough then you will eventually get a buffer underflow or overflow error. You should always check for
errors and exit the loop if an error occurs.
Figure 21. Example block diagram code for single USRP (channel) continuous acquisition
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Multiple Channel, Continuous
Application: Broadband spectrum monitoring, MIMO transmission and reception
Example VI Name: niUSRP EX Rx Multiple Synchronized Inputs.vi
The following table lists out the VIs that you will use for this type of application. Note that some VIs are
required, others can be added for more advanced functionality and some are not applicable.
NI-USRP VI
Open Session
Configure Signal
Initiate
Fetch/Write Data
While Loop
USRP Property Node
Abort
Close Session
Acquire








Transmit






The multiple channel continuous example is an extension of the continuous example that is set up for
multiple USRPs (channels). Multiple USRPs allow you to obtain a larger system bandwidth by using the
individual USRPs at separate frequencies. To configure a full MIMO system, you invoke a LabVIEW
property node and use the MIMO cable or synchronize to an external clock source.
Figure 22. Example block diagram code for multiple channel continuous acquisition
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Avant de commencer : l'environnement LabVIEW
Avant de commencer, il est important que vous soyez à l'aise avec l'environnement LabVIEW. Il s'agit
d'un langage de programmation “G” - pour graphique - utilisé par des milliers d'ingénieurs à travers le
monde pour concevoir des applications de petite et moyenne envergures, ainsi que des applications de
type système.
L'interface utilisateur graphique du programme s'appelle la “Face-avant” et correspond à la fenêtre
grise de l'environnement LabVIEW. Vous pouvez déposer des commandes, des boutons rotatifs, des
interrupteurs, des graphes, des graphes déroulants, des LED, et bien d'autres éléments courants qui
permettent à l'utilisateur/opérateur de contrôler le programme.
L'interface de programmation ou de codage s'appelle “diagramme” et correspond à la fenêtre blanche.
En tant que programmeur, vous pouvez placer une multitude de fonctions et de sous-routines afin de
déterminer la fonctionnalité de votre programme. LabVIEW dispose de milliers de fonctions prédéfinies qui vous permettent de gagner du temps en réutilisant les fonctions les plus prisées et en
accédant rapidement aux matériels.
Figure 23. Un VI LabVIEW simple avec une face-avant (sur la gauche) et un diagramme (sur la droite)
Pour en savoir plus et vous familiariser avec ce logiciel, le moyen le plus rapide est un portail gratuit en
ligne créé pour les étudiants et appelé Self-Paced Video Training for Students (Vidéos d'auto-formation
destinées aux étudiants).
Pour de plus amples détails, reportez-vous à la section Options de formation supplémentaires à la fin
de ce document.
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Préparer LabVIEW
Remarque : cet exercice part du principe que vous avez déjà installé tous les logiciels conformément à
ce qui est décrit dans les sections précédentes. Si ce n'est pas le cas, veuillez vous référer à la section
appropriée.
Objectifs :
Configurer l'environnement LabVIEW pour une programmation facile
Instructions :
1. Lancez LabVIEW en naviguant jusqu'à Démarrer » Tous les programmes »
National Instruments » LabVIEW 2013 » LabVIEW
2. Sur la fenêtre de démarrage LabVIEW, naviguez jusqu'à Outils » Options…
a. Dans la catégorie Face-avant, choisissez ‘Style Argent’ pour la soussection Style des commandes des nouveaux VIs. Tous les nouveaux
indicateurs et commandes déposés sur la face-avant auront le look
argent modernisé
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Lorsque vous programmerez, votre face-avant ressemblera à ceci :
b. Dans la section correspondant à la catégorie Diagramme,
désélectionnez ‘Nouveaux terminaux sous forme d'icônes’ dans la
sous-section Paramètres généraux pour nettoyer le diagramme et
gagner de la place
c. Cliquez sur OK et fermez cette fenêtre
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3. Sur le diagramme, effectuez un clic droit dans l'espace blanc pour afficher la
palette des fonctions, puis un clic gauche sur la punaise en haut à gauche de
la palette pour la fixer à l'écran
a. Une fois celle-ci fixée, un nouveau bouton apparaît pour Personnaliser.
Effectuez un clic gauche sur ce nouveau bouton et sélectionnez
Changer les palettes visibles...
b. Cliquez sur le bouton Tout désélectionner.
c. Cliquez sur les cases à cocher correspondant à Programmation, E/S
de mesure, E/S d'instruments, Mathématiques, Traitement du signal,
et RF Communications, puis cliquez sur OK
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4. Passez à la face-avant et changez les palettes visibles en Moderne, Argent,
Traitement du signal, et RF Communications
5. Cliquez sur le bouton OK pour fermer la boîte de dialogue des palettes visibles
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Raccourcis LabVIEW
Le tableau ci-dessous recense les raccourcis clavier disponibles dans l'environnement LabVIEW.
Reportez-vous à la Carte de référence rapide LabVIEW pour obtenir une version PDF des raccourcis
clavier.
Frappe de clavier
Ctrl + C
Description
Copier l'élément ou les éléments sélectionnés
Ctrl + V
Coller l'élément ou les éléments sélectionnés
Ctrl + X
Couper l'élément ou les éléments sélectionnés
Ctrl + Z
Annuler
Ctrl + Espace
Activer le placement rapide
Ctrl + H
Activer/désactiver l'Aide contextuelle
Ctrl + B
Supprimer tous les fils de liaison brisés du diagramme
Ctrl + E
Naviguer entre un diagramme et sa face-avant
Ctrl + R
Exécuter le VI sélectionné
Ctrl + S
Enregistrer le VI sélectionné
Ctrl + T
Mosaïque verticale des fenêtres de la face-avant et du
diagramme
Ctrl + U
Nettoyer le diagramme
Ctrl + cliquer et
glisser
Insérer un espace vide sur le diagramme
Tableau 2. Raccourcis clavier LabVIEW
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Travaux Pratiques
Création d'une radio FM logicielle
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Exercice1 : Trouver une station radio
Remarque : cet exercice part du principe que vous avez déjà installé tous les logiciels et configuré tous
les matériels.
Objectifs
Partie A
a) Utiliser un exemple pour trouver toutes les stations de radio dans la région
b) Analyser ces stations de radio en utilisant le graphe de la face-avant
1. Sur le bureau, ouvrez le dossier niUSRP Hands-on
a. À l'intérieur du dossier Exercise, ouvrez Exercise 1A.VI
2. Configurez la face-avant comme suit :
Paramètre
Valeur
Device names
192.168.10.2
IQ Rate
10M
Carrier frequency
93M
Active antenna
RX1
Gain
1
Number of samples
20k
Timeout
10
Remarque : faites attention à la différence entre M et m. LabVIEW interprète m comme
milli et M comme méga
3. Appuyez sur la flèche d'exécution et vous verrez un graphe similaire à celui cidessous. Si vous n'avez pas un assez grand nombre de pics dans votre graphe,
arrêtez le programme, modifiez le gain (jusqu'à 30) et exécutez-le à nouveau
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4. Vous regardez une portion du spectre d'une radio FM. En France, chaque station
radio se voit attribuer une fréquence centrale comprise entre 87,5 MHz et 108 MHz.
Observons une seule et même station
Remarque : votre graphe de fréquence aura une autre apparence que celui illustré cidessus car l'activité des stations de radio dépend des régions.
5. Sur le tracé Frequency, cliquez sur l'icône magnifier, puis à partir du menu local
cliquez sur l'icône centrale située en haut
6. Choisissez une station de radio sur le graphe, puis faites glisser votre curseur de la
gauche vers la droite autour du pic
7. Sur cette illustration, la station de radio FM va environ de 2,6 MHz à 2,8 MHz. La
bande passante de cette station est de 200 kHz, ce qui sera notre nouvelle fréquence
IQ. La fréquence centrale de cette station est à +2,7 MHz de notre fréquence
porteuse actuelle de 93 MHz (95,7M)
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8. Pour régler uniquement cette station
a. Arrêtez le programme
b. Définissez carrier frequency à 95,7M
c. Définissez IQ rate à 200k
Remarque : cette station peut ne pas être active dans votre région mais le même
processus reste valable pour les autres
9. Exécutez à nouveau le programme et observez les modifications du Frequency Plot
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Exercice 2 : Démoduler une radio FM
Remarque : cet exercice part du principe que vous avez déjà installé tous les logiciels et configuré tous
les matériels.
Objectifs
a) Acquérir, représenter sous forme de graphe et écouter une station de radio FM
b) Comprendre les paramètres qui contrôlent la façon dont un programme acquiert les
données
c) Découvrir les principes du flux de données LabVIEW
Partie A
1.
Naviguez jusqu'au dossier Exercises
a. Lancez Exercise 2A.VI
2. Sur la barre de menus, sélectionnez Fenêtre»Afficher le diagramme
a. Les fonctions et VIs nécessaires pour démoduler, représenter sous forme
de graphe et écouter la station de radio FM sont déjà placés sur le
diagramme. Vous allez devoir les connecter dans le bon ordre pour mener
à bien cet exercice
3. À l'intérieur de la boucle While, trouvez le VI niUSRP Fetch Rx Data (poly)
a. Câblez la sortie data à l'entrée z de la fonction Complex To Polar
4. Câblez la sortie theta de la fonction Complex To Polar à l'entrée Phase du VI Unwrap
Phase
(Assurez-vous que vous n'avez pas câblé la sortie r)
5. Câblez Phase déroulée à l'entrée X du VI Derivative x(t)
6. Câblez la sortie dX/dt à l'entrée Y de la fonction Build Waveform
7. Câblez waveform en sortie à plusieurs blocs :
a. à l'entrée z de la fonction Complex To Re/Im
b. à l'entrée signal temporel du VI FFT Power Spectrum and PSD
c. à input waveform du VI Simple Resample
8. Câblez output waveform du VI Simple Resample à l'entrée data du VI Simple Sound
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9. Configurez la carte son
a. Câblez le bloc bleu en bas à gauche de la boucle While à l'entrée task ID
du VI Simple Sound
b. Câblez le bloc jaune à error in du VI Simple Sound
10. Sur la barre de menus, sélectionnez Fenêtre»Afficher la face-avant
11. Enregistrez le VI et nommez-le Exercise2A.vi
12. Exécutez le VI
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Figure 24. Face-avant achevée
Figure 25. Diagramme achevé
Explication sur le flux de données
2
1
4
3
Flux de données
5
2
1
3
6
1. Le terminal device names est relié à une commande
de la face-avant et fournit l'adresse IP de l'USRP
2. Ce VI crée un lien de communication entre le
programme et l'USRP. Il retourne un descripteur de
session sur le fil de liaison violet.
3. Le VI Configure définit les paramètres pour
l'acquisition de notre signal. Ces paramètres
proviennent de plusieurs commandes différentes sur
la face-avant. Les paramètres réels utilisés par
l'USRP (contraints) sont affichés par les indicateurs
de la face-avant.
4. Le VI Initiate indique à l'USRP qu'il doit commencer
à acquérir les données.
5. Le VI Simple Sound vous permet d'ouvrir, d'écrire ou
de fermer la carte son en fonction de l'Action
spécifiée.
1. Le VI Fetch Rx Data acquiert un
certain nombre d'échantillons
(number of samples) du buffer de
réception.
2. Ces trois VIs et fonctions effectuent la
4
démodulation FM.
3. La fonction Build Waveform prend la
valeur dt du VI Fetch Rx Data de façon
à ce que le tracé de la FFT et celui de
l'IQ s'adaptent correctement à
5
l'échelle de l'axe des x.
4. Représente les composantes I et Q
sur un seul et même tracé du graphe.
5. Représente la FFT du signal sous
forme de graphe.
6. Ré-échantillonne les données
démodulées à 44,1 kHz pour la carte
son.
3
4
2
1. Le VI Simple Sound ferme la carte son pour permettre aux
autres programmes de l'utiliser.
2. Le VI Merge Errors combine plusieurs fils de liaison
d'erreur provenant de branches de code parallèles.
3. Le VI Abort cesse d'acquérir les données et le VI Close
Session libère toute mémoire utilisée.
4. Affiche toutes les erreurs sur un indicateur de la face-avant.
1
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Explication sur l'algorithme
Le principe qui sous-tend la modulation de fréquence (FM) est que l'amplitude d'un signal analogique
fait varier la fréquence d'un signal porteur. Il existe des équations bien connues qui modélisent un
modulateur de fréquences en tant que modulateur de phase et vice-versa. Nous préférons une
équation en termes de phase car la phase est facile à obtenir à partir d'un signal IQ en utilisant la
fonction arc tangente.
Où fc est la porteuse démodulée, kf est la sensibilité de la fréquence et
m(t) est le signal de message
Intégrer le signal FM en fonction du temps et multiplier par 2π nous donne
0
L'USRP se charge de la conversion par abaissement de fréquence RF, de sorte que fc est désormais
égale à zéro et que notre premier terme est éliminé de l'équation ci-dessus. Il ne reste que la
constante sensible à la fréquence kf multipliée par l'intégrale du signal de notre message m(t). Si nous
pouvons obtenir la phase θi(t) de la forme d'onde IQ, alors nous pouvons prendre la dérivée pour
récupérer notre signal de message m(t).
Nous nous heurtons à un problème car la sortie de l'arctangent est aux alentour de ±180 degrés. Nous
pouvons résoudre ce problème en ajoutant des multiples de 360 degrés de sorte que la différence de
phase ne sera jamais interrompue. Cela s'appelle le déroulement de phase.
Dans l'image ci-dessous, le signal sur le graphe de gauche est limité entre -180 degrés et +180
degrés. Le signal sur la droite illustre la phase d'un signal déroulé de 0 à +720 degrés.
Figure 26. Comparaison d'un signal original et d'un signal déroulé
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Figure 27. Tracé de fréquence illustrant un signal FM démodulé
Figure 28. Image provenant de l'entrée Wikipedia intitulée FM Broadcasting 2
Figure 28 montre le graphe du spectre de fréquence idéal d'une station de radio FM qui a été
démodulée. Le bloc sur le côté gauche de 30 Hz à 15 kHz est le son que nous écoutons dans nos hautparleurs. Lorsque nous ré-échantillonnons la forme d'onde pour notre carte son, tout ce qui va au-delà
de l'audio mono est filtré.
Il y a une tonalité pilote de 19 kHz qui signifie l'existence d'audio stéréo. Cet audio centré à 38 kHz
peut être décalé en bande de base, puis ajouté ou soustrait à l'audio mono pour obtenir les voies
stéréo gauche ou droite.
Il y a d'autres signaux numériques à droite qui ne seront pas abordés dans cette session.
2
FM broadcasting. (16 janvier 2013). Wikipedia, l'encyclopédie libre. Daté du 17:13, 16 janvier 2013,
sur http://en.wikipedia.org/w/index.php?title=FM_broadcasting&oldid=533382011
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Objectifs
a) Utiliser un script de fichier .m pour démoduler une station de radio FM en utilisant
MathScriptRT
b) Comprendre la multiplicité des modèles de calculs de LabVIEW
Partie B
1. Remplacez les fonctions de démodulation par un nœud MathScript
a. Supprimez Complex To Polar, Unwrap Phase, Derivative x(t) et la
constante Backward
b. Appuyez sur <Ctrl-B> pour supprimer tous les fils de liaison brisés
2. Placez un nœud MathScript
a. Effectuez un clic droit sur un espace blanc vide
b. Naviguez jusqu'à Programmation » Structures et cliquez sur Nœud
MathScript
c. Placez le nœud MathScript à l'endroit où se trouvaient les fonctions de
LabVIEW que vous venez de supprimer
3. Cliquez avec le bouton droit sur la bordure du nœud MathScript
a. Cliquez avec le bouton droit sur la bordure du nœud MathScript et
choisissez Import
b. Naviguez jusqu'au dossier Exercises
c. Sélectionnez le script FMdemod.m
4. Cliquez avec le bouton droit sur la bordure gauche du nœud MathScript et choisissez
Ajouter une entrée
a. Dans la prochaine boîte de texte qui apparaît saisissez samples
5. Cliquez avec le bouton droit sur la bordure droite du nœud MathScript et cliquez sur
Add Output » fmdemod
6. Naviguez jusqu'à la palette Programmation » Waveform
a. Placez une fonction Obtenir les composantes d’une waveform à gauche
de l'entrée des échantillons MathScript
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b. Câblez la sortie data du VI niUSRP Fetch Rx Data à l'entrée de la fonction
Obtenir les composantes d’une waveform
c. câblez la sortie Y à l'entrée samples
7. Câblez la sortie fmdemod à l'entrée Y de la fonction Build Waveform
8. Enregistrez le VI et nommez-le Exercise 2B
9. Revenez à la face-avant et exécutez le VI
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Figure 29. Face-avant achevée
Figure 30. Diagramme achevé
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Objectifs
a) Démoduler rapidement une station de radio FM à l'aide du Toolkit LabVIEW
Modulation
b) Utiliser des propriétés intellectuelles (IP) existantes issues de toolkits pour accomplir
rapidement des tâches
Partie C
1. Supprimez la fonction Obtenir les composantes d’une waveform, le nœud MathScript
et la fonction Build Waveform
2. Appuyez sur <Ctrl-B> pour supprimer tous les fils de liaison brisés
3. Cliquez sur la flèche vers le bas du VI niUSRP Fetch Rx Data
a. Sélectionnez Single Channel » Complex Double Cluster
4. Faites apparaître la palette des fonctions
a. Naviguez jusqu'à RF Communications » Modulation » Analog »
Demodulation
b. Faites glisser la deuxième icône (MT Demodulate FM) sur le diagramme à
l'endroit où se trouvait le nœud MathScript
5. Câblez la sortie data de niUSRP Fetch Rx Data à l'entrée FM modulated waveform du
VI MT Demodulate FM
6. Câblez FM demodulated waveform à plusieurs blocs :
a. à l'entrée z de la fonction Complex To Re/Im
b. à l'entrée signal temporel du VI FFT Power Spectrum and PSD
c. à input waveform du VI Simple Resample
7. Enregistrez le VI et nommez-le Exercise 2C
8. Revenez à la face-avant et exécutez le VI
Astuce : vous devrez peut-être effectuer un clic droit sur le tracé de la fréquence et
mettre automatiquement à l'échelle l'axe des y
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Figure 31. Face-avant achevée
Figure 32. Diagramme achevé
Exercice 3 : Communications numériques
Remarque : cet exercice part du principe que vous avez déjà installé tous les logiciels et configuré tous
les matériels.
Remarque : assurez-vous d'avoir connecté un câble de rebouclage et un atténuateur 30 db avant
d'émettre tout signal.
Objectifs
a) Ouvrir et exécuter un exemple de communications numérique
b) Identifier les portions du diagramme et les éléments du processus de
modulation/démodulation
Partie A
1. Faites équipe avec la personne ou le groupe à côté de vous pour décider qui va ouvrir
le VI transmis et qui va ouvrir le VI reçu
2. Dans le dossier Exercises, ouvrez soit le VI USRP Packet Receiver, soit le VI USRP
Packet Transmitter
3. Configurez l'émetteur
a. Passez à l'onglet Tx Parameters
b. Assurez-vous que les paramètres IQ Sampling Rate et Frequency sont
identiques à ceux du récepteur
c. Passez à l'onglet Specify Modulation
d. Assurez-vous que le même schéma de modulation est utilisé pour la
réception
e. Passez à l'onglet Specify Packet
f. Assurez-vous que la structure des paquets est la même sur le récepteur
g. Cliquez sur l'onglet Rx Display
4. Configurez le récepteur
a. Passez à l'onglet Rx Parameters
b. Assurez-vous que les paramètres IQ Sampling Rate et Frequency sont
identiques à ceux de l'émetteur
c. Passez à l'onglet Specify Modulation
d. Assurez-vous que le même schéma de modulation est utilisé pour
l'émission
e. Passez à l'onglet Specify Packet
f. Assurez-vous que la structure des paquets est la même sur l'émetteur
g. Cliquez sur l'onglet Specify Message
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5. Cliquez sur la flèche d'exécution
Remarque : vous devez redémarrer le programme pour que les modifications apportées
aux commandes de la face-avant soient effectives.
6. Cliquez pour revenir à l'onglet Specify Modulation et modifiez la modulation de QPSK
à BPSK ou 8-PSK et observez les modifications du Constellation Graph sur l'émetteur
et le récepteur
Remarque : des schémas de modulation d'ordre élevé sont susceptibles de nécessiter
des optimisations telles que la pré-distorsion numérique qui n'est pas abordée dans ce
cours
7. Exécutez à nouveau ce VI avec le nouveau schéma de modulation
Figure 33. Signal numérique BPSK
Figure 34. Signal numérique QPSK
Figure 35. Signal numérique 8-PSK
Figure 36. Signal numérique Offset QPSK
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On Your Own Exercise 4: LabVIEW Tips and Tricks
Goals
Part A
a) Learn about time saving features in LabVIEW
b) Make LabVIEW graphs more interactive
This exercise should be completed on your own, after the hands-on class to give you
more familiarity with the LabVIEW development environment
Tools Palette
By default, LabVIEW selects tools for you based on the context of your cursor. If you
need more control over which tool is selected, use the Tools palette to select a specific
tool to operate or to modify front panel and block diagram objects
1. Select View » Tools Palette to display the Tools palette
2. To display a temporary version of the Tools palette at the location of the cursor
Press the <Shift> key and right-click
3. You can disable automatic tool selection by clicking the Automatic Tool Selection
button on the Tools palette, shown as follows
a. When you click the Automatic Tool Selection button to disable automatic
tool selection, you can either select a tool on the palette or use the <Tab>
key to move through the most commonly used tools in the sequence they
appear on the palette. When you select a tool, the cursor changes to
correspond to the icon of the tool
b. To return to automatic tool section, press the <Tab> key or click the
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Automatic Tool Selection button to enable automatic tool selection again
4. You can configure LabVIEW to disable automatic tool selection and move through
the most commonly used tools whenever you press the <Tab> key and to toggle
automatic tool selection only when you press the <Shift-Tab> keys or click the
Automatic Tool Selection button
a. Select Tools » Options to display the Options dialog box, select
Environment from the Category list, and remove the checkmark from the
Lock automatic tool selection checkbox
Automatically Wiring Objects
As you move a selected object close to other objects on the block diagram, LabVIEW
draws temporary wires to show you valid connections. When you release the mouse
button to add the object to the block diagram, LabVIEW automatically connects the
wires. You also can automatically wire objects already on the block diagram. LabVIEW
connects the terminals that best match and does not connect the terminals that do not
match
1. Toggle automatic wiring by pressing the spacebar while you move an object
using the Positioning tool. By default, automatic wiring is enabled when you
select an object from the Functions palette or when you clone an object already
on the block diagram. Automatic wiring is disabled by default when you use the
Positioning tool to move an object already on the block diagram. When
automatic wiring is enabled, the selected object retains its appearance when you
drag it. When automatic wiring is disabled, the selected object appears as a
dotted outline when you drag it
a. If necessary, enable automatic wiring and set the maximum and
minimum distances for objects to wire automatically
b. Add a numeric control to the front panel window
c. Press the <Ctrl-E> keys to display the block diagram. (Mac OS X) Press
the <Command-E> keys. (Linux) Press the <Alt-E> keys
d. Select the Add function from the Functions palette
e. Move the left side of the function close to the right side of the numeric
control terminal on the block diagram. As you move the function close to
the terminal, LabVIEW draws temporary wires to show you valid
connections. Make sure the function is within the maximum and
minimum distances you set in step 1
f. When a temporary wire appears between the numeric control terminal
and the top left terminal of the Add function, click the mouse button to
add the function and wire the objects
g. Make sure you wire all required terminals. Otherwise, the VI is broken
and will not run. Use the context help window to see which terminals a
block diagram node requires. The labels of required terminals appear bold
in the Context Help window
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LabVIEW Graphs vs. Charts
Graphs and charts differ in the way they display and update data. VIs with a graph
usually collect the data in an array and then plot the data to the graph. This process is
similar to a spreadsheet that first stores the data then generates a plot of it. When the
data is plotted, the graph discards the previously plotted data and displays only the new
data. You typically use a graph with fast processes that acquire data continuously. In
contrast, a chart appends new data points to those points already in the display to create
a history. On a chart, you can see the current reading or measurement in context with
data previously acquired. When more data points are added than can be displayed on the
chart, the chart scrolls so that new points are added to the right side of the chart while
old points disappear to the left. You typically use a chart with slow processes in which
only a few data points per second are added to the plot
Figure 37. Waveform Chart and Graph after 1 Run
Figure 38. Waveform Chart and Graph after 5 Runs
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Customizing Graphs
Each graph includes options that you can use to customize the graph to match your data
display requirements. For example, you can modify the behavior and appearance of
graph cursors or configure graph scales. The following illustration shows the elements of
a graph
1
2
3
4
5
Plot Legend
Cursor
Scale legend
Cursor mover
Cursor legend
6
7
8
9
10
11
Minor Grid Mark
Grid Mark
X-scale
Graph Palette
Y-scale
Label
You can add the plot legend, scale legend, cursor legend, graph palette, and label by
right-clicking the graph, selecting Visible Items from the shortcut menu, and selecting
the appropriate element
Working with Graphs
You should follow this exercise after running the program in Exercise 2 and stopping the
program so there is data on your plot to work with
1. Add the graph palette to the waveform graph
a. Right-click the graph
b. Select Visible Options » Graph Palette
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2. Zoom into the 19 kHz pilot tone
a. Click the magnifier icon (center) to bring up the zoom menu
b. Choose the Zoom Vertical Selection option (center top)
c. Create a selection by clicking on the left side of the 19 kHz tone and
dragging a box to the right side of the tone
d. We can repeat this procedure until we can get the X-axis to give us a
better approximation of the frequency, but let’s use a cursor instead
3. Show the Cursor Legend by right-clicking the waveform graph and navigating to
Visible Items
a. Right-click inside the cursor palette and select Create Cursor » SinglePlot to create a cursor that is bound to the plot on the graph
b. Change from the zoom tool to the select tool by clicking the first icon on
the graph palette
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c. Grab the vertical yellow line and drag it on top of the pilot tone
d. Does the cursor tell you the frequency is around 19 kHz?
Sometimes you may expect LabVIEW to work in a certain way but it doesn’t. We just
learned how to use the zoom vertical selection, to zoom in to a particular region of a
waveform, but we did this while the program was not running
1. Click the run arrow to run the program
2. Change back to the zoom vertical selection tool
3. Try to zoom in. What happens? For a very small amount of time, the graph did
zoom in, but it “reset.” What actually happened is the x-axis and the y-axis auto
scaled. To have the ability to zoom in to the waveform as the program is
running you should turn off auto scaling
4. Right click the x-axis numbers
5. From the shortcut menu, unselect AutoScale X
6. Do the same for the y-axis
7. Try to zoom back in with the program still running. Does it work now?
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Additional Training
Self-Paced Video Training for Students
Use this set of step-by-step tutorials, example projects, and short videos to get started with NI tools.
Begin by learning how to work within the LabVIEW environment. Understand how to work within the
NI LabVIEW software environment. Watch video modules to learn the fundamental building blocks of
programming in LabVIEW. Test your understanding of LabVIEW concepts with the LabVIEW Basics
Test and assess your understanding of programming within the LabVIEW environment by completing
the LabVIEW Basics Exercise.
Visit ni.com/academic/students/learn-labview to learn the basics of LabVIEW today!
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Professional Training Options
There are many courses that we offer for training in LabVIEW, as well as our Data Acquisition and
other hardware platforms. We also offer three levels of LabVIEW certification along with a few other
certification paths. These can help to boost your resume, and also solidify your knowledge of NI
software and hardware.
NI Certification Path
For more information, visit ni.com/training today. Be sure to ask about our special pricing for academic
customers.
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Appendix A: Exercise Solution Screenshots
Exercise 1
No programming necessary
Exercise 2 A
Exercise 2 B
Exercise 2 C
Exercise 3
No programming necessary
Exercise 4
No programming necessary
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Glossary A: RF & Communication Reference
Symbols
Degrees
dB
Decibel
Hz
Hertz
Ohms
/
per
V
Volts
W
Watts
A
Amplitude Modulation
(AM)
A process that varies the amplitude of a radio frequency (RF) carrier signal
according to the amplitude of the message signal.
Amplitude-Shift Keying
(ASK)
Refers to a type of amplitude modulation, which assigns bit values to
discrete amplitude levels. The carrier signal is then modulated among the
members of a set of discrete values to transmit information.
analog signal
An analog signal is any continuous signal for which the time varying
feature (variable) of the signal is a representation of some other time
varying quantity.3
ADC
Analog-to-Digital Converter—A hardware component that converts analog
voltages to digitized values. An ADC can convert an analog signal to a
digital signal representing equivalent information.
3
Analog signal. (2013, January 11). In Wikipedia, The Free Encyclopedia. Retrieved 18:33, January 16, 2013,
from http://en.wikipedia.org/w/index.php?title=Analog_signal&oldid=532543697
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B
bandwidth
The measure of a circuit or transmission channel to pass a signal without
significant attenuation over a range of frequencies. Bandwidth can also
refer to the information rate (in bits per second) that can pass through a
circuit or transmission channel.
baseband signal
The baseband is the range in the frequency spectrum occupied by the
unmodulated message signal. Both the message signal and the
downconverted complex I/Q signal are referred to as baseband signals.
binary signal
A signal that carries information by varying between two possible
values, corresponding to 0 and 1 in the binary system.
C
carrier
The signal that carries the information encoded or modulated on it.
Typically, the carrier is a fixed frequency sine wave, which can be
amplitude-, phase-, or frequency-modulated.
carrier frequency
The frequency of the carrier signal that is a sinusoidal signal upon which
the desired signal to be transmitted is modulated. The sinusoidal signal
"carries" the modulation.
Carson's rule
Defines the approximate modulation bandwidth required for a carrier
signal that is frequency-modulated by a spectrum of frequencies rather
than a single frequency. The Carson bandwidth rule is expressed by the
relation CBR = 2(Δf + f m) where CBR is the bandwidth requirement, Δf is
the carrier peak deviation frequency, and f m is the highest modulating
frequency.
CCDF
The Complementary Cumulative Distribution Function (CCDF) is a
statistical characterization of the time-domain waveform that completely
describes the power characteristics of a signal.
center frequency
The middle frequency of the channel bandwidth. In frequency modulation,
the center frequency is equal to the rest frequency —specifically, the
frequency of the unmodulated carrier wave.
complex envelope
A complex representation of the baseband modulated signal.
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component (I/Q)
The real (I—in-phase) and imaginary (Q—quadrature) parts of a complex
number are referred to as components . The Modulation Toolkit VIs can
use complex components to describe signal properties. Use the NI-USRP
functions Write Tx Data VI and NI-USRP Fetch Data VI in applications that
use Modulation Toolkit VIs, because they also use complex components.
For example, you can represent a two-dimensional vector of length S by
its components S = A + iB , where A and B are the vector x- and ycomponents. The real part of the vector corresponds to the x-component
(A ), while the imaginary part corresponds to the y-component (B ).
D
DC offset
A complex signal impairment that shifts the locus of ideal symbol
coordinates off-center in the I/Q plane. A DC offset can be added to the
baseband I component, the Q component, or both. The DC offset can be
either positive or negative, with the sign indicating direction of the shift.
DC offset is expressed as a percentage of full scale, where "full scale" is
the amplitude of the baseband QM waveform.
DAC
Digital-to-analog converter—An electronic device, often an integrated
circuit, that converts a digital number into a corresponding analog voltage
or current.
Decoding
Data decoding involves removing redundant bits from the sequence and
correcting for any errors that might have happened during transmission.
The signal decoding process is usually more complicated than the
encoding process and can be very computationally intensive.
demodulation
Describes the recovery from a modulated wave of a signal having the
same characteristics as the original message signal.
The down converted signal undergoes a demodulation process. This step
is the opposite of modulation and refers to the process required to extract
the original information signal from the modulated signal
dB, decibel
The unit for expressing a logarithmic measure of the ratio of two signal
levels: dB = 20 log10(V1/V2), for signals in volts.
dBm
decibel milliwatt—Absolute power level referenced to 1 mW.
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downconverter
A signal conditioning device that converts a specific band of highfrequency (RF) signals to lower, more manageable intermediate
frequencies (IF) that can be digitized.
Down conversion
The first step in the demodulation process is down conversion from a real
passband waveform to a complex I/Q baseband waveform. This process
involves mixing the real-valued passband waveform with a locally
generated carrier tone, followed by lowpass filtering to generate the I/Q
baseband waveform.
DSP
Digital Signal Processing—The computation of signal or system transfer
characteristics using numeric algorithms. Examples of areas where DSP
techniques may be applied include: digital filters, echo detection or echo
cancellation, speech synthesis, FFT for spectrum analysis, correlation
computations, imagine recognition, and servo-feedback control.
E
encoding
A data source generates the information signal sent to a particular receiver.
This signal may be either an analog signal, such as speech, or a digital
signal, such as a binary data sequence. The information signal is typically a
baseband signal represented by a voltage level.
equalization
In an adaptive feed-forward equalizer, the taps of a filter that acts as an
equalizer that continuously adapts its coefficients to compensate for the
action of the channel filter. At the start of the equalization process, you
typically supply training bits to train the equalizer. After training, the
equalizer switches to decision-directed feedback mode, where the
equalizer trains itself based on its own decisions.
F
fetch
Process that transfers data from device onboard memory to PC memory.
filtering
In a digital communication system, digital information can be sent on a
carrier through changes in its fundamental characteristics such as phase,
frequency, and amplitude. In a physical channel, these transitions can be
smoothed, depending on the filters implemented during transmission. In
fact, filters play an important part in a communications channel because
they can eliminate spectral leakage, reduce channel width, and eliminate
adjacent symbol interference known as inter-symbol interference (ISI).
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FIR filter
Finite Impulse Response (FIR) is a term that describes a filter with no
feedback elements, hence, its impulse response is finite. In contrast, IIR
(infinite impulse response) circuitry does use feedback. FIR filters can be
implemented by using analog or digital shift registers, or by using software
algorithms. For a tutorial of IIR and FIR filters, search for digital filter in
the NI Developer Zone.
FFT
The Fast Fourier Transform (FFT) is an efficient algorithm often used for
spectrum analysis.
FM
Frequency Modulation (FM) is a process that varies the frequency of a
sinusoidal carrier wave from a center frequency by an amount proportional
to the instantaneous value of the message signal. In FM, the center
frequency is the carrier frequency.
FPGA
A Field-Programmable Gate Array (FPGA) is a semi-conductor device
which contains a large quantity of gates (logic devices), which are not
interconnected, and whose function is determined by a wiring list, which
is downloaded to the FPGA. The wiring list determines how the gates are
interconnected, and this interconnection is performed dynamically by
turning semiconductor switches on or off to enable the different
connections. Search for FPGA in the NI Developer Zone for a more
complete explanation.
frequency
Frequency refers to a basic unit of rate measured in events or oscillations
per second. Frequency also refers to a number representing a specific
point in the electromagnetic spectrum. Frequency is measured as the
number of cycles per unit time. The SI unit of measure for frequency is
Hertz (Hz) where 1 Hz equals one cycle per second.
frequency span
Typically refers to a range of frequencies, for example from 10 kHz to 20
kHz. This term often describes the range that an instrument, such as a
spectrum analyzer, is set to measure, or the range over which a set of
frequencies of interest are located. For example, an FM modulated signal
may cover a span from 100.5 MHz to 100.7 MHz.
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G
gain
The factor by which a signal is amplified, often expressed in dB. Gain as a
function of frequency is commonly referred to as the magnitude of the
frequency response function.
H
Hertz, Hz
Hz is the SI unit for measurement of frequency. One Hertz (Hz) equals one
cycle per second. It can be used to represent the number of scans read or
updates written per second.
I
IIR filter
Infinite Impulse Response Filter—A filter that is designed using feedback
or storage elements so that its impulse response will, in principle, last
forever. In contrast, FIR filters have a finite impulse response.
impairments
All transmission media (including wireless, fiber optic, and copper)
introduce some form of distortion (impairments) to the original signal.
Different types of channel models have been developed to mathematically
represent such real-world distortions.
in-phase signal
The I (in phase) component of a signal is typically the real component of a
complex-valued signal.
I/Q data
The translation of the magnitude and phase data of a signal from a polar
coordinate system to a complex Cartesian (X,Y) coordinate system. The I
(In-phase) component is typically the real-valued component of the signal,
while the Q component is typically the imaginary component of the signal.
I/Q modulation
In-Phase/Quadrature Modulation (I/Q modulation) is a modulation
technique where a signal is modulated by two signals 90 degrees out of
phase with each other.
I/Q signal
A control signal for changing an RF carrier signal.
IF
Intermediate Frequency (IF)—In radio receivers or spectrum analyzers, the
original high-frequency signal is often mixed to an intermediate frequency
before demodulation.
information signal
Contains the data for transmission. The information signal is used to
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modulate the carrier wave to create the modulated wave for transmission.
The information signal data is recovered from the modulated wave by a
process of demodulation.
The information signal is often referred to as the baseband signal or
message signal .
impedance
The electrical characteristic of a circuit that opposes flow of current
through that circuit. It can be expressed in ohms and/or
capacitance/inductance.
intersymbol interference
In telecommunication, intersymbol interference (ISI) is a form
of distortion of a signal in which one symbol interferes with subsequent
symbols. This is an unwanted phenomenon as the previous symbols have
similar effect as noise, thus making the communication less reliable. ISI is
usually caused by multipath propagation or the inherent non-linear
frequency response of a channel causing successive symbols to "blur"
together.4
ISM
The Industrial, Scientific and Medical (ISM) bands are low-power radio
frequencies for industrial, scientific, and medical processes, and licensefree wireless communication.
L
Local Oscillator (LO)
Local Oscillator refers to an internal oscillator in a radio, receiver, or
instrument that tunes the frequency of the device. The local oscillator is
mixed with a fixed frequency oscillator, which generates a sum and
difference component.
M
message signal
Contains the data for transmission. The message signal is used to
modulate the carrier wave to create the modulated wave for transmission.
The message signal data is recovered from the modulated wave by a
process of demodulation.
The message signal is often referred to as the baseband signal or
information signal .
4
Intersymbol interference. (2012, December 15). In Wikipedia, The Free Encyclopedia. Retrieved 18:54, January 16, 2013,
from http://en.wikipedia.org/w/index.php?title=Intersymbol_interference&oldid=528200950
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MIMO
Multiple input, multiple output—A measurement technique, most often
used in acoustics and vibration, to identify signal paths and frequency
response functions from multiple inputs to multiple outputs. Associated
with this measurement class are the techniques of partial and multiple
coherence, which help identify which parts of an output signal are due to a
specific input signal or combinations of signals.
modulation
A process, or the result of a process, by which characteristics of a carrier
wave are altered according to information in the baseband signal to
generate a modulated wave that is transmitted.
In a diagram of the components of a Software Defined Radio system, the
modulation block converts the information signal bit stream into in-phase
(I) and quadrature phase (Q) data components. This block typically also
involves pulse shaping to minimize intersymbol interference and reduce
bandwidth.
P
passband
The range of frequencies that a device can properly propagate or measure.
phase
The fraction of the wave cycle which has elapsed relative to the origin5
phase-locked loop (PLL)
An electronic circuit that controls an oscillator so that the circuit maintains
a constant phase angle relative to a reference signal.
PPS
Pulse Per Second
pulse-shaping filter
By applying a pulse-shaping filter to the modulated sinusoid, sharp
transitions in the signal are smoothed and the resulting signal is limited to
a specific frequency band. In addition, pulse-shaping filters are applied to
communication signals to reduce intersymbol interference.
5
Phase (waves). (2012, December 25). In Wikipedia, The Free Encyclopedia. Retrieved 19:02, January 16, 2013,
from http://en.wikipedia.org/w/index.php?title=Phase_(waves)&oldid=529664818
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Q
quadrature signal
The Q (quadrature) component of a complex-valued signal is typically the
imaginary-valued component of the signal.
QAM
Quadrature-Amplitude Modulation (QAM) is a form of quadrature
modulation in which the two carriers are both amplitude-modulated.
R
radio frequency (RF)
Refers to the radio frequency range of the electromagnetic spectrum. RF
is often used to describe a range of sub-infrared frequencies from the tens
of MHz to several GHz.
reference clock
Clock to which a device phase locks another, usually faster, clock. A
common source for the Reference clock is the 10 MHz oscillator present
on the PXI backplane.
RX, Rx
Receive data or signals. RX refers to the hardware receiver; Rx refers to
receive operations in software.
S
sample rate
The rate at which a device acquires an analog signal, expressed in
samples per second (S/s). The sample rate is typically the clock speed of
the analog-to-digital converter (ADC).
SDR
Software-Defined Radio
SerDes
Serializer/Deserializer
SFDR
Spurious Free Dynamic Range—The separation or distance, expressed in
dB, from the amplitude of the fundamental frequency and the next highest
spur.
SMA
A small type of threaded coaxial signal connector typically used in higher
frequency applications.
symbol rate
Expresses the number of symbols transmitted per second (symbols/s). To
convert symbol rate into bit rate, which expresses the number of bits
transferred per second, multiply the symbol rate by the number of bits per
symbol used in the digital modulation scheme of interest. Symbol rate is
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also known as baud rate .
T
TTL
Transistor-Transistor Logic—A digital circuit composed of bipolar
transistors wired in a certain manner. A typical medium-speed digital
technology. Nominal TTL logic levels are 0 and 5 V.
TX, Tx
Transmit data or signals. TX refers to the hardware transmitter; Tx refers
to transmit operations in software.
U
UHD
Universal Hardware Driver, a software driver that is called on by the
LabVIEW driver to provide control over a connected USRP device.
USRP
Universal Software Radio Peripheral—A computer-hosted hardware
peripheral used to create software-defined radio systems.
upconverter
A signal conditioning device that converts a specific band of IF frequencies
to high-frequency (RF) signals.
Upconversion
In a diagram that shows the components of a Software Defined Radio, the
baseband modulated signal undergoes analog up conversion to frequencytranslate the signal to the RF frequency at which the signal is transmitted.
V
VDC
Voltage Direct Current
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