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

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Presentation Transcript
what is sdr
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

history
History

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

problem
Problem

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

solution
Solution

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

Keep code modular (C++ classes)‏

transmitter
Transmitter

Coder Block

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

Bit/Symbol

Convert the data stream into transmission symbols for transmission

Transmit Filter

Shape the symbols to the desired waveform

Modulator

Modulate the signal for transmission

channel
Channel

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

Interference

Other interference modeled as normal random variables

receiver
Receiver

LNA/AGC

Amplify signal to receiver circuit levels

Sampler

Sample the received signal for digital processing

Demodulator

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

Equalizer

Distortion compensation

Decoder

Decode symbols into appropriate bit stream

software algorithm development process
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
Implementation Decisions

C++

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++

Linux

Documentation

Cross-Platform

Macintosh and IBM Compatible

modularity
Modularity

Utilities Class

AM Modulation

Class

QA Modulation

Class

FM Modulation

Class

Transceiver

Transmitter

Receiver

modulation techniques
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
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
Frequency Modulation (FM)
  • V(t) = Vocos(2ft + )‏
    • For FM f is varied.
quadrature am
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.

digital modulation
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

BPSK, QPSK, …

matched filters
Matched Filters
  • Maximize the SNR to improve QoS
  • Receiver filter is matched to the transmitter filter by the relationship
carrier and timing recovery
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
Spectrum Digital DSP Boards

SDI TMS320C6713 DSP Boards

  • 225 MHz
  • 512KB Flash
  • 8MB SDRAM
  • Microphone, Speaker, Mono In/Out audio ports
  • USB Interface
preliminary testing
Preliminary Testing

MATLAB simulation using AM modulation

Receiver rectifies signal and detects peaks

Raw Signal

Demodulated Signal

thank you
Thank you!

We appreciate your time and thank you for coming!

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