An Introduction to Software Defined Radio With LabVIEW and NI...

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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

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e C

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Ch

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din

g

Mo

dula

tion

Up

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rsio

n

Dow

nconve

rsio

n

De

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Ch

an

nel D

eco

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So

urc

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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