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 DescriptionHardware-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 gain-bandwidth 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 open-source 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 expensiveRangeSNRUser Interface

Toward Implementation Software Design: GNU Radio

Two Hardware Possibilities:Hardware Design – see our various reportsUSRP – “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 ReferencesHuseyin 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.u-ryukyu.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/exploring-gnuradio.html, November 2004.

http://www.arrl.org/files/file/Hambands_color.pdf

McNair, Bruce. “EE585WS Class Notes.” Stevens Institute of Technology, Spring 2011