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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)

July 10, 2008 Flynn/Katz - SDR

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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