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An Introduction to Software Defined Radio With
LabVIEW and NI USRP
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Hands-on Course Objectives
Exercise 1
• Find an FM radio station using the USRP as spectrum analyzer
• Introduction to the LabVIEW environment
• Configuring the USRP software defined radio
• Exploring live radio spectrum
Exercise 2
• Demodulate & listen to live FM radio
• LabVIEW programming fundamentals
• Integrating digital signal processing functions
• Using .m file script inside LabVIEW
Exercise 3
• Explore a digital communications system
• Open and run a digital communications reference design
• Identify the part of a more advanced LabVIEW block diagram
• Overview of the modulation & demodulation process
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• LabVIEW Communications is an integrated, hardware-aware design environment for prototyping communications systems that streamlines prototyping by offering a single, cohesive environment that enables both the processor and FPGA programming
What is LabVIEW Communications?
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The National Instruments Vision
“To do for test and measurement
what the spreadsheet did for financial analysis.”
Virtual Instrumentation
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SDR Algorithm Prototyping Applications
Utilities & Infrastructure
Medical Devices & Internet of Things
Aerospace & Defense
Automotive & Car to Car
Communications & RF Identification
Research Topics
Data rate
Capacity
Power Consumption
Coexistence
Security
Monitoring
Land Mobile & Safety Radio
Satellite Comm & Navigation
Education
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The Next 30 Years: Expanding LabVIEW into System Design
Research & Modeling
Design & Simulation
Verification & Validation
Manufacturing
Product Verification Design Verification
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From Concept to Prototype … Rapidly!
Design Simulate Prototype
Graphical System Design Platform
• LabVIEW Graphical System Design offers one tool, integrated flow • Shorter learning curve • Easier system integration • Reduce the time to hardware … rapid prototyping!
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Software and Hardware Introduction
Find an FM radio station using the USRP as spectrum analyzer
Introduction to the LabVIEW environment
Configuring the USRP software defined radio
Exploring live radio spectrum
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Getting Started in LabVIEW
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1 2
2
3 4
Viewing, Creating, and Interacting with Documents
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1
2
3
4
Storing and Retrieving Data
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2
1
3
4
Creating a Way to Display Data
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3
4
1
3
2
Creating Code
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5
4 3 4
6
1 2
7
Configuring a VI for Use As a SubVI
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Getting Help
1
2
3
4
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Software-Defined Radio (SDR) refers to the
technology wherein software modules running on
a generic hardware platform are used to
implement radio functions …..1
What is a Software Defined Radio?
[1] http://www.sdrforum.org/pages/documentLibrary/documents/SDRF-06-R-0011-V1_0_0.pdf
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NI USRP Software Defined Radio
1 Gigabit Ethernet to PC Plug-and-play capability Up to 25 MS/s baseband IQ
streaming
Tunable RF Front Ends Frequency Range
50 MHz – 2.2 GHz (NI-2920) 2.4 GHz & 5.5 GHz (NI-2921) 400 MHz – 4.4 GHz (NI-2922)
Signal Processing and Synthesis Develop and explore
algorithms with NI LabVIEW
Simulate and process live signals with NI Modulation Toolkit
Multi Device Synchronization Easy 2X2 Synchronization Expandable to 8X8 or more
GPS Disciplined Clock Option Increased Frequency
Accuracy
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NI USRP Software Defined Radio
RF Transceiver
Software Processing
Baseband IQ
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SDR Components
Tx • Digital to Analog
• RF Upconversion • Modulation
• RF Downconversion
• Analog to Digital Rx
• Demodulation
• Signal Processing
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NI USRP-2920 Hardware Diagram
Analog RF Transceiver Fixed Function FPGA PC
4. Antenna
5. Gain
2. IQ Rate
6. # Samples/ Buffer
3. Carrier Frequency
1. Device Name
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1. Device Name – IP address of one or multiple USRP
2. IQ Rate – Quadrature sampling rate, equivalent to bandwidth
3. Carrier Frequency – Frequency of interest
5. Gain – Amplification of signal before digitizing the signal
4. Antenna – Select which antenna port to receive from
6. Fetch size – how many samples to acquire each fetch
USRP Configuration in 6 Parameters
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USRP Configuration in 6 Parameters
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NI USRP RF Receive Parameters
Frequency
Pow
er
(dB
)
94.7 MHz
1 MHz
50 MHz
IQ Rate ~ Bandwidth ~
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NI USRP RF Receive Parameters
Frequency
Pow
er
(dB
)
94.7 MHz
1 MHz
50 MHz
Carrier Frequency
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NI USRP RF Receive Parameters
Frequency
Pow
er
(dB
)
94.7 MHz
1 MHz
50 MHz
Gain
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NI USRP RF Receive Parameters
number of samples
timefetchsamplesnumberrateIQ
__*_
1
bandwidthresolutionsamplesnumber
rateIQ_
_
_
Frequency Domain
Time Domain
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Exercise 1 Find a Radio Station using Captured Data
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• What is the center frequency of the radio station you found?
• What is the bandwidth of the radio station?
• How do you set the receive bandwidth of the USRP?
• How can you receive a weak signal better ?
Exercise 1: Quiz
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Demodulating Live FM
Demodulate & listen to live FM radio
LabVIEW programming fundamentals
Integrating digital signal processing functions
Using .m file script inside LabVIEW
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• Block diagram execution
– Dependent on the flow of data
– Does NOT execute left to right
• Nodes execute when data is available to ALL input terminals
• Nodes supply data to all output terminals when done
Dataflow Programming
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NI-USRP Driver Software
Initialize Configure Start Read IQ Stop Close
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Common Data Types Found in LabVIEW
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Reviewing the Block Diagram
Wire: Complex Cluster
Wire: Error Cluster
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• The complex cluster data type is used to display and store periodic signal measurements.
Complex Cluster Data Type
t0 – Initial time of waveform
dt – Sample period
Y – Array of data samples
Baseband IQ : Y is an array of complex numbers representing I and Q samples
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• An array consists of elements and dimensions
• Elements: data that make up the array
• Dimension: the length, height, or depth of an array
• Consider using arrays when you work with a collection of similar data and when you perform repetitive computations
Arrays
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Loops
• While Loop • Terminal counts iterations
• Runs at least once
• Runs until stop condition is met
• For Loop • Terminal counts iterations
• Runs according to input of count terminal
While Loop
For Loop
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FM radio can be demodulated in 3 steps:
1. Calculate carrier phase (Arc tan of baseband IQ data)
2. Unwrap the phase (remove discontinuities)
3. Compute the derivative (change in phase ≈ frequency)
Demodulating Broadcast FM Radio
Baseband IQ
Calculate phase
Unwrap phase
Differentiate phase
Demodulated FM
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Exercise 2A Demodulate and Listen to FM Radio
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• Why did we unwrap the phase?
• How many samples per second are coming from the USRP?
• Why is there a spike near 20 KHz?
Exercise 2A: Quiz
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Demodulated Broadcast FM
30 Hz
15 kHz
38 kHz
67.65 kHz
92 kHz
100 kHz
0
19 kHz Stereo Pilot
Stereo Audio Left - Right
Direct Band
RBDS
Mono Audio Left + Right
Audos Subcarrier
57 kHz
FM broadcasting. (n.d.). In Wikipedia, Retrieved from http://en.wikipedia.org/wiki/FM_broadcasting
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• Implement equations and algorithms textually
• Input and output variables created at the border
• Generally compatible with popular .m file script language
• Terminate statements with a semicolon to disable
immediate output
MathScript Node
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Detect phase
Unwrap phase
Differentiate phase
Frequency Demodulation Algorithm
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Exercise 2B Use a MathScript RT node
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• Why did we use the Get Waveform Components function?
• Are there any differences in using the MathScript node vs LabVIEW functions?
• If we deleted the graphs, would the music still play?
Exercise 2B: Quiz
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Exercise 2C Use LabVIEW Communications IP
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• Are there any differences in the graph when using the Modulation Toolkit function vs MathScript or LabVIEW?
• What happens if we specify an FM deviation of 75,000 Hz?
Exercise 2C: Quiz
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Digital Communications
Explore a digital communications system
Open and run a digital communications reference design
Identify the part of a more advanced LabVIEW block diagram
Overview of the modulation & demodulation process
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So
urc
e C
od
ing
Ch
an
ne
l Co
din
g
Mo
dula
tion
Up
co
nve
rsio
n
Dow
nconve
rsio
n
De
mo
dula
tion
Ch
an
nel D
eco
din
g
So
urc
e D
eco
din
g
Communications Channel
Digital Communication System
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NI Modulation Toolkit
NI Modulation Toolkit
Digital Communication System
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NI Modulation Toolkit
NI Modulation Toolkit
NI USRP
NI USRP
Digital Communication System
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Packet-based Communication Link System Setup
• USRP control (Tx & Rx) • Modulate Tx signal • Demodulate Rx signal • Reconstruct message
NI USRP-2920
Receiver NI USRP-2920
Transmitter
RF Signal
Center Frequency: 915MHz Modulation Format: PSK packets Bit Rate: 100kbps
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Packet-based Communication with LabVIEW
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Packet Structure
GUARD
BAND SYNC
SEQ PCKT
NUM PAD DATA
Field Length [bits]
Description
Guard Band 30 Allow initialization of Rx PLL, filters, etc
Sync Sequence 20 Frame and Symbol Synchronization
Packet Number 32 Range: 0-255 Used for reordering of packets and detection of missing packets
Data 128 Variable length data field. Length detected dynamically at Rx end
Pad 20 Allows for filter edge effects.
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Transmitter Block Diagram
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The Received Signal
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Receiver Block Diagram
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Exercise 3 Packet Based Transceiver
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Receiver: Pipelined Shift Register Architecture
Acquire
Detect & Slice Packets
Resample and Demodulate
Synchronize & Decode
Reconstruct Data
Accumulate & Display Packets
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Receiver: Pipelined Shift Register Architecture
Acquire
Detect & Slice Packets
Resample and Demodulate
Synchronize & Decode
Reconstruct Data
Accumulate & Display Packets
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• How many packets do you send out using the default message?
• Why doesn’t the receiver stop if you change the message?
• What happens if you change the modulation scheme on the transmitter but not the receiver?
• Why do we need the packet slicer on the receiver?
Exercise 3: Quiz
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NI SDR User Solutions Wireless Comms Education
Record and Playback
Cognitive Radio
Physical Layer Prototyping
Compensating for RF nonlinearities with DSP
8x8 MIMO
Direction Finding
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RF Record & Playback
• Record and play back up to 20 MHz of bandwidth
• Repeatable testing of algorithms / devices on realistic dataset
• Supplement a PXI lab with low-cost playback at your desk
Re
co
rd
Pla
yb
ack
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NI USRP Research Case Study:
Cognitive Radio & Whitespace
Large Scale Cognitive Radio Testbed • Prototyping cognitive radio in LabVIEW
• Spectral sensing with blind detection
• Database driven geo-location with GPS
• Deployed in Munich, Germany
“LabVIEW software and the NI USRP hardware are key components of this research project, allowing the team to rapidly prototype and successfully deploy the first cognitive radio test bed of this kind.” Dr. Paulo Marques, COGEU
Aveiro, Portugal
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WiFi Physical Layer Prototyping
• Continuously monitoring multiple wifi channels
• Demodulation and descrambling of 802.11b beacon signals
• Identification of hotspots, tracking relative power levels
Carrier Detection
Frequency Offset
Estimation & Correction
Demodulation &
Descrambling
Interpret the frame for
SSID
Demodulate Descramble
Dr. Murat Torlak
802.11b SSID Decoding
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NI USRP Research Case Study:
NI USRP 8x8 MIMO Testbed • Adaptable from 2x2 to 8x8
• Algorithm design in MathScript RT
• 128 subcarrier OFDM, 4 QAM, spatial diversity
• Independently clocked, phase coherent Tx & Rx
Dr. Robert Heath Director WNCG University of Texas at Austin
MIMO
Cable
USRP
Rx 1 USRP
Rx 2
MIMO Cable
USRP
Rx 3 USRP
Rx 4
MIMO
Cable
USRP
Rx 5
USRP
Rx 6
MIMO
Cable
USRP
Rx 7
USRP
Rx 8
PPS in
Ref in External
Clock
Network
Cable
Network
Cable
Network
Cable
Host
Compute
r
Transmit
Receive
MIMO
Cable
USRP
TX 1 USRP
TX 2
MIMO Cable
USRP
TX 3 USRP
TX 4
MIMO
Cable
USRP
TX 5
USRP
TX 6
MIMO
Cable
USRP
TX 7
USRP
TX 8
Gigabit
Ethernet
Switch
External
Clock
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6x6 MIMO Testbed
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Position Detection & Localization
• Testing MUSIC direction finding algorithm
• Rapid prototyping in LabVIEW with MathScript RT
• Synchronized up to12 USRP devices
• Reference provides continuous phase alignment compensation
Calibration Signal
USRP RX 1
PPS in Ref in
External Clock
Network Cable
Network Cable
Host Computer
Gigabit Ethernet Switch
USRP RX 2
USRP RX 3
USRP RX 4
USRP TX
Direction Finding (uniform linear array)
Prof. Athanassios Manikas
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LabVIEW Communications Community
8x8 MIMO-OFDM GPS Simulation
RF Record & Playback RF Direction Finding &
Localization
Tx
ni.com/sdr
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Summary
• LabVIEW offers a graphical approach, shortening the design process, and tight hardware/software integration that allows for seamless transition from design to test • NI provides a full spectrum of RF / Communications solutions: RF Test, Research and Education • LabVIEW and NI USRP is an accessible, easy-to-use software defined radio platform
