Matt Schurmann
Erik Thompson
Jon Pirog
Scott Curtis
Overview
Introduction
 Functional Description
 Technical Description
 Performance Objectives
 Implementation Alternatives
 Toward Senior Design
 Conclusion
 References

SDR? Amateur Radio? Say What?
Traditional radio implementations use
fixed-function hardware to implement
protocol stacks
 Today an estimated 16,000 amateur
hardware-based radio repeaters exist in
the USA

A Repeater
What is Software Defined Radio?

SDR is a radio architecture that seeks to
implement as much of its functionality as
possible in digital baseband software

Ideally, SDR is 100% re-configurable.
Flexible RF hardware receives,
transmits and performs A/D conversion.
Software does everything else
Functional Description
Hardware-Based Radio
Software Defined Radio
Images: Bruce McNair, EE585WS, Spring 2011, Stevens Institute of Technology
Functional Description (cont’d)

Two fundamental sections:

RF Frontend – Interface between air and
baseband processing

Baseband Processing – perform
modulation (FM for amateur radio),
demodulation, coding, error correction,
waveform synthesis, RF hardware tuning.
Interface with user, internet, data link layer
Functional Description (cont’d)
Implementation Issues

Current ADC technology doesn’t allow
high-rate, high precision frequency.

Remember the Nyquist Frequency?
Digitizing a 1.3 GHz signal, means
sampling over 2.6 GHz!

Work-around: superheterodyning
Superheterodyning
Wideband Hardware

The amateur radio bands in the USA
range from about 1 MHz to 1.3 GHz

Amplifiers are limited by gainbandwidth product. High gain = low
bandwidth

Similar concerns exist for mixers, filters
Baseband Hardware

Baseband hardware design pits
Power vs. Re-configurability

Compromise: Hybrid FPGA and
Microcontroller hardware design

Which programming language to use? C
for Microcontroller, VHDL for FPGA
Baseband Software

Baseband software for waveform
synthesis and modulation will require
intense digital signal processing
(DSP)

Saving Grace: GNU Radio – an opensource software radio library using C
and Python!
Performance Objective

To implement an SDR-based amateur
radio repeater prototype

It must have competitive performance,
even if it is more expensive
 Range
 SNR
 User Interface
Toward Implementation

Software Design: GNU Radio

Two Hardware Possibilities:
 Hardware Design – see our various reports
 USRP – “Universal Software Radio
Peripheral.” Available through Stevens SDR
Lab
Tradeoff – Cost, Time, Complexity vs. Learning
Opportunity, Impressiveness of Project
USRP
Custom Design
RF Receiver Schematic
Altera Cyclone FPGA
Demo Board
Conclusion

SDR-based Amateur Radio Repeater

Many design tradeoffs, and constraints
due to cost, time, current technology

More information: http://mjsch.org/d6

Questions?
Selected References
Huseyin Arslan and Hasari Celebi, "Software Defined Radio Architectures for Cognitive
Radios," in Cognitive Radio, Software Defined Radio, and Adaptive Wireless Systems.:
Springer, 2007, ch. 4, pp. 109-144.
Tom Wada. (2005) All Digital FM Receiver. [Online]. http://www.ie.uryukyu.ac.jp/~wada/design05/spec_e.html
Mahababul Hansan, Md Khan, and Farzana Akhter, "Design and Implementation of a QPSK
Demodulator," BRAC University, Bangladesh, 2010.
Behzad Ravazi, RF Microelectronics. Upper Saddle River: Prentice , 1998.
Technologies, Wipro. "Software Defined Radio Whitepaper." 2002.
http://www.broadcastpapers.com/whitepapers/WiproSDRadio.pdf (accessed February
25, 2011).
E. Blossom, "Exploring GNU Radio," http://www.gnu.org/software/gnuradio/doc/exploringgnuradio.html, November 2004.
http://www.arrl.org/files/file/Hambands_color.pdf
McNair, Bruce. “EE585WS Class Notes.” Stevens Institute of Technology, Spring 2011