Software Defined Radio Project

Software Defined Radio Project James Flynn Sharlene Katz

Overview  

Independent Study / Graduate Projects

 

Summer Calendar

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What is Software Defined Radio?

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Advantages of Software Defined Radio

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Traditional versus SDR Receivers

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SDR and the USRP

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Preparation for Next Meeting

July 10, 2008

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Independent Study/Projects Fall – Independent Study – Timing   Summer/Fall schedule  

     

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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

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Radar and Threat detection

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Electronic Intelligence (ELINT)

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Radio Astronomy

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Amateur Radio Flynn/Katz - SDR

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Future SDR Applications  

Personal Communications      

 

Cell phones Wi Fi Entertainment distribution

Public Safety    

Remote Sensing Communications    

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Information, graphics Voice Flynn/Katz - SDR

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Future SDR Applications  

Broadcasting  

Digital Radio

 

Digital Television

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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

Flynn/Katz - SDR

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No more standards  

Interoperability problem solved  

Military  

 

Public Safety  

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Example: Operation Market Garden 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.  

     

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Temperature Humidity Vibration

No alignment issues.

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The sky’s the limit…  

“Smart” radio technology

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Encoding, processing and decoding not constrained by component limitations.

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More efficient use of limited spectrum.

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Users always have the latest, best implementation.

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Automated, plug-and-play systems.

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Features tailored for individual, time-variable preferences/needs.

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Traditional Receiver RF Amplifier

|fLO-fc| fLO+fc

x

IF Amplifier

fLO Local Oscillator

10 KHz

530 980

fc

Demodulator 10 KHz f (KHz) 5

10 KHz

f (KHz) 455

f (KHz)

1700

f (KHz)

10 KHz

455

fLO=1435 KHz 530 980 July 10, 2008

f (KHz)

1700

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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 Receiver Front End Traditional / Hardware Receiver

RF Amplifier

Current SDR Receiver

IF Amplifier

x

Demodulator

Local Oscillator

Receiver Front End

Future SDR Receiver ?

ADC

ADC

Software

Software Flynn/Katz - SDR

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SDR Receiver Using the USRP Motherboard

Daughterboard

Receiver Front End similar to traditional front end with fIF = 0

ADC

FPGA

USB Controller

Decimation, MUX, +

PC GNU Radio software

Interface to PC

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 July 10, 2008

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Extracting I(t) from S S(t) = I(t)cos(2π fct) + Q(t)sin(2π fct) Multiplying both sides by cos(2πfct): S(t)cos(2π fct) = I(t)cos 2 (2π fct) + Q(t)sin(2π fct)cos(2π fct) I(t) Q(t) = 1 + cos(4π fct)] + [ [sin(4π fct) + sin(0)] 2 2 1 1 1 = I(t) + I(t)cos(4π fct) + + Q(t)sin(4π fct) 2 2 2

Applying this signal to a low pass filter, the output will be: 1 I(t) 2 July 10, 2008

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Extracting Q(t) from S S(t) = I(t)cos(2π fct) + Q(t)sin(2π fct) Multiplying both sides by sin(2πfct): S(t)sin(2π fct) = I(t)cos(2π fct)sin(2π fct) + Q(t)sin 2 (2π fct) I(t) Q(t) = sin(4π fct) − sin(0)] + [ [1 − cos(4π fct)] 2 2 1 1 1 = I(t)sin(4π fct) + Q(t) − Q(t)cos(4π fct) 2 2 2

Applying this signal to a low pass filter, the output will be: 1 Q(t) 2 July 10, 2008

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USRP Receiver Front End x fc

RF Amplifier (0 – 20 dB)

LPF

I

LO

90°

x

LPF

Q

USRP front end translates the signal to zero frequency and extracts I and Q July 10, 2008

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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  

∆t

ADC

Sampling Interval: Δt = July 10, 2008

1 = 0.0156µS 64 × 10 6

Quantization Levels: Δv =

Flynn/Katz - SDR

2 = 0.488mV 212

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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

July 10, 2008

fs = 64Msamp/sec

Flynn/Katz - SDR

64M = 128 500K

fs = 500Ksamp/sec

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SDR Receiver with USRP Daughterboard

Motherboard I

FPGA (Decimator, MUX, etc.)

ADC

USB PC Controller

Q

GNU Radio Software July 10, 2008

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USRP - Motherboard/ Daughterboard

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GNU Radio Software    

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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 Flynn/Katz - SDR

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Design of a Receiver USRP  

GNU Radio Application

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

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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) Flynn/Katz - SDR July 10, 2008 27  

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