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Software Defined Radio Project
James Flynn Sharlene Katz
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Overview Independent Study / Graduate Projects
Summer Calendar
What is Software Defined Radio?
Advantages of Software Defined Radio
Traditional versus SDR Receivers
SDR and the USRP
Preparation for Next Meeting July 10, 2008 Flynn/Katz - SDR
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Independent Study/Projects
Fall – Independent Study – Timing Summer/Fall schedule
Meeting times – every two weeks Goals Presentations
Projects
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What is Software Defined Radio (SDR)? • A new technology for implementing radio
communications systems
• Art and science of building radios using
software
• Eliminating hardware and moving software as
close to the antenna as possible
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Current SDR Applications
Military Agile, robust and secure communications systems
Radar and Threat detection
Electronic Intelligence (ELINT)
Radio Astronomy
Amateur Radio
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Future SDR Applications
Personal Communications Cell phones Wi Fi Entertainment distribution
Public Safety Remote Sensing Communications
Information, graphics Voice
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Future SDR Applications
Broadcasting Digital Radio
Digital Television
Advantages of SDR
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No more standards
Historical Problems with standards Inertia
AM to FM Stereo Broadcasting AM to SSB communications AM to FM communications Black and White to Color Television Analog Color Television to HDTV AM/FM Analog to HD radio broadcasting
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No more standards
Interoperability problem solved Military
Example: Operation Market Garden Public Safety
Example: 9/11
Modes and operation tailored to individual needs rather than choosing from a few standards.
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Reliability Fewer components = less failures Remote repair/update. No aging. No environmental drift.
Temperature Humidity Vibration
No alignment issues.
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The sky’s the limit… “Smart” radio technology Encoding, processing and decoding not constrained
by component limitations. More efficient use of limited spectrum. Users always have the latest, best implementation. Automated, plug-and-play systems. Features tailored for individual, time-variable
preferences/needs.
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Traditional Receiver
Local Oscillator
RF Amplifier
IF Amplifier
x Demod- ulator
fc
fLO
|fLO-fc| fLO+fc
f (KHz) 530 1700 980
10 KHz
f (KHz) 530 1700 980
10 KHz f (KHz) 455
10 KHz
fLO=1435 KHz
455 f (KHz)
10 KHz f (KHz)
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Disadvantages of the Traditional Receiver
Simple modulation / demodulation only Limited implementation of filters Alignment Aging Complexity Fixed design: frequency/mode Non linearity – unwanted signals
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Traditional vs. SDR Receiver
RF Amplifier
IF Amplifier
x Demod- ulator
Local Oscillator
Receiver Front End
Traditional / Hardware Receiver
Software Receiver Front End ADC Current SDR Receiver
Software ADC
Future SDR Receiver ? July 10, 2008 Flynn/Katz - SDR
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SDR Receiver Using the USRP
Receiver Front End ADC USB
Controller FPGA PC
Daughterboard Motherboard
similar to traditional front end with fIF = 0
Decimation, MUX, +
Interface to PC
GNU Radio software
USRP: Universal Software Radio Peripheral
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Quadrature Signal Representation
The received signal, S(t), may be represented as follows: S(t) = I(t)cos(2π fct) +Q(t)sin(2π fct)
fc = carrier frequency
I(t) = in-phase component
Q(t) = quadrature component
Contain amplitude and phase information of baseband signal
• GNU Radio software uses I and Q components to demodulate signals
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Extracting I(t) from S S(t) = I(t)cos(2π fct) +Q(t)sin(2π fct)
S(t)cos(2π fct) = I(t)cos2 (2π fct) +Q(t)sin(2π fct)cos(2π fct)
=I(t)21+ cos(4π fct)[ ] + Q(t)2 sin(4π fct) + sin(0)[ ]
=12I(t) + 1
2I(t)cos(4π fct) + +
12Q(t)sin(4π fct)
Multiplying both sides by cos(2πfct):
Applying this signal to a low pass filter, the output will be: 12I(t)
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Extracting Q(t) from S S(t) = I(t)cos(2π fct) +Q(t)sin(2π fct)
S(t)sin(2π fct) = I(t)cos(2π fct)sin(2π fct) +Q(t)sin2 (2π fct)
=I(t)2
sin(4π fct) − sin(0)[ ] + Q(t)2 1− cos(4π fct)[ ]
=12I(t)sin(4π fct) +
12Q(t) − 1
2Q(t)cos(4π fct)
Multiplying both sides by sin(2πfct):
Applying this signal to a low pass filter, the output will be: 12Q(t)
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USRP Receiver Front End
RF Amplifier (0 – 20 dB)
x LPF
90°
x LPF
LO fc
I
Q
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USRP front end translates the signal to zero frequency and extracts I and Q
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Analog to Digital Converter (ADC) 12 bit A/D Converter (212 levels) 2 volt peak-peak maximum input 64 Msamp/second
ADC
∆t
Δt =1
64 ×106= 0.0156µS Δv =
2212
= 0.488mVQuantization Levels: Sampling Interval:
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Decimation Original sampling rate is 64Msamp/sec Converts a portion of spectrum 32 MHz wide Generally we are interested is a narrower portion of the
spectrum requiring a lower sampling rate USB cannot handle that high data rate (up to 256 Mbps/32
MBps/8 M complex samp/sec Occurs in the FPGA of the USRP
fs = 64Msamp/sec fs = 64Msamp/sec fs = 500Ksamp/sec 64M500K
= 128
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SDR Receiver with USRP
ADC FPGA
(Decimator, MUX, etc.)
USB
Controller PC
I
Q
Daughterboard Motherboard
GNU Radio Software
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USRP - Motherboard/Daughterboard
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GNU Radio Software Community-based project started in 1998 GNU Radio application consists of sources (inputs), sinks
(outputs) and transform blocks Transform blocks: math, filtering, modulation/
demodulation, coding, etc. Sources: USRP, audio input, file input, signal generator,
… Sinks: USRP, audio output, file output, FFT, oscilloscope,
… Blocks written in C++ Python scripts used to connect blocks and form application
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Design of a Receiver
USRP: Set frequency of local oscillator (receive frequency), gain of amplifier, decimation factor
GNU Radio application: use Python to specify and connect blocks that perform demodulation and decoding
USRP GNU Radio Application
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Final Thoughts References: http://www.csun.edu/~skatz
Go to: Areas of interest Software Defined Radio Project [Login: gnuradio password: usrp]
Date of next meeting User list Preparation for next meeting
Analog to Digital Converter (signal levels, sampling rates, quantization levels, etc.)
RFX 400 Daughterboard (how it works, signal levels, TX and RX channels)
FPGA (block diagram, what it includes, programming) July 10, 2008 Flynn/Katz - SDR