Interpolation: A First Step in Teaching Rate Conversion

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Interpolation A First Step in Teaching Rate
Conversion
Thad Welch United States Naval Academy Michael
Morrow University of Wisconsin-Madison Cameron
Wright University of Wyoming
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Presentation Overview

• Motivation/introduction
• Hardware description
• Interface and control software
• System operation
• System performance
• Classroom use
• Conclusions and questions

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Motivation/introduction

• Goal - teach digitally implemented SDR (software
  defined radio)
• Problems is that the boards needed to support
  these operations are expensive and typically cost
  over 10,000 apiece
• We started with the transmitter
• Rate conversion is required to go from baseband
  sample frequencies to the carrier sample
  frequencies

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For Example

• If we are using 16-QAM, with a data rate of 150
  kbps, and 4 samples per symbol, this results in a
  baseband sample frequency of 150 kHz
• If we select an RF carrier frequency of 1 MHz,
  with a 12 MHz RF sample frequency, the resulting
  interpolation factor is 80
• 80 12 MHz/150 kHz
• Changing the sample frequency is relatively easy,
  but there are consequences

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Complete System
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AD9857 Block Diagram
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Adapter Board and FPGA Card
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winDSK6 with comm_RF
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Comm_RF GUI
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System Block Diagram
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FGPA Daughtercard Logic
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Spectrum of the Example
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Recovered Constellation
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Classroom Use

• Previous offering of our DSP course have
  discussed decimation and interpolation, but have
  not included RF hardware
• This system can reinforce the theoretical or
  MATLAB-based discussions of this topic
• This is not a trivial step and having
  interface/control software allows for rapid
  parameter selection
• System is relatively easy to use and provides a
  complete SDR transmitter

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Interpolation A First Step in Teaching Rate
Conversion
Thad Welch (t.b.welch_at_ieee.org) United States
Naval Academy Michael Morrow (morrow_at_ieee.org)
University of Wisconsin-Madison Cameron Wright
(c.h.g.wright_at_ieee.org) University of Wyoming