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A Modular Approach. Software Defined Radio. What is SDR?. Software Defined Radio

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Software Defined Radio

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A Modular Approach

Software Defined Radio

What is SDR?

Software Defined Radio

“A radio communication system which can potentially tune to any frequency band and receive any modulation across a large frequency spectrum by means of as few as hardware possible and processing the signals through software” (Wikipedia, “Software Defined Radio”)‏

One device serves multiple purposes

Significant utility in military and cellular markets

Precursor to “Cognitive Radio”

Radio will alter transmission and reception parameters (modulation, frequency, and power) to avoid interference and improve overall QoS


Many wireless devices are designed to serve a single purpose

Cell phone, wireless router, GPS receiver, AM/FM radio, etc.

Many current software radio groups exists

GNURadio, HPSDR, SDR Forum, and others


Design a software defined radio that has the ability to:

Change modulation techniques “on-the-fly”

Avoid unwanted white noise

Provide a means to easily implement the same software on other radios


Code and implement on a DSP various algorithms that provide the desired functionality of the radio

Keep code modular (C++ classes)‏

Block Diagram of a SDR


Coder Block

Add bits to data stream to provide error protection (data redundancy)‏


Convert the data stream into transmission symbols for transmission

Transmit Filter

Shape the symbols to the desired waveform


Modulate the signal for transmission


Channel properties

Model a wireless channel with an appropriate transfer function

White Noise

WSS random process modeled as a process with a constant power spectral density


Other interference modeled as normal random variables



Amplify signal to receiver circuit levels


Sample the received signal for digital processing


Demodulate the received signal

Carrier Recovery

Recover the phase of the carrier signal

Matched Filter

Filter designed to match the transmitting filter

Timing Recovery

Recover original clock of the transmitter


Distortion compensation


Decode symbols into appropriate bit stream

Software AlgorithmDevelopment Process

Algorithms will be

Developed in MATLAB

Tested in SIMULINK

Converted to C/C++

Tested in C/C++ model

Compared to SIMULINK

Verified on DSP board

Implementation Decisions


Ease of transition between MatLab and C++

C++ will provide modular classes and functions

Inheritance and Virtual Functions

DSP Boards can be programmed with C/C++




Macintosh and IBM Compatible


Utilities Class

AM Modulation


QA Modulation


FM Modulation





Radio Software Design


Modulation Techniques

Software Defined Radios allow for multiple modulation techniques

NO additional hardware is needed

Filtering can also be accomplished without any additional hardware.

Amplitude Modulation (AM)‏

V(t) = Vocos(2ft + )‏

For AM the value Vo is varied to change the amplitude of the signal.

Frequency Modulation (FM)

  • V(t) = Vocos(2ft + )‏

    • For FM f is varied.

Quadrature AM

V(t) = Vocos(2ft + ) +

Vosin(2ft + )‏

For QAM, two signals that are out of phase by 90 degrees are used simultaneously.

QAM Waveform

Digital Modulation

The techniques that were discussed are for analog modulation.

The process is similar for digital modulation

The digital modulation types are: ASK, FSK, and QASK

Once these techniques are realized, they can be adapted to achieve other modulation types


Matched Filters

  • Maximize the SNR to improve QoS

  • Receiver filter is matched to the transmitter filter by the relationship

Carrier and Timing Recovery

Data aided vs. Non-data aided

  • Data Aided

  • Only applicable when data symbols are detected reliably

  • Requires phase and frequency information of the carrier

  • Based on decisions made by receiver

  • Non-Data Aided

  • Independent of data symbols

  • Can be used for both tracking and acquisition

  • Not as accurate as Data-aided while tracking

Spectrum Digital DSP Boards

SDI TMS320C6713 DSP Boards

  • 225 MHz

  • 512KB Flash


  • Microphone, Speaker, Mono In/Out audio ports

  • USB Interface


Preliminary Testing

MATLAB simulation using AM modulation

Receiver rectifies signal and detects peaks

Raw Signal

Demodulated Signal

Any Questions?

Thank you!

We appreciate your time and thank you for coming!

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