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November 16, 2007
Jonathan HawsBlair Leonard
Khemmer PorterJoshua Templin
Software Defined RadioA Modular Approach
November 16, 2007 2
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
November 16, 2007 3
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
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Problem
• Design a software defined radio that has the ability to:
1. Change modulation techniques “on-the-fly”
2. Avoid unwanted white noise3. Provide a means to easily implement
the same software on other radios
November 16, 2007 5
Solution
• Code and implement on a DSP various algorithms that provide the desired functionality of the radio
• Keep code modular (C++ classes)
November 16, 2007 6
Block Diagram of a SDR
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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
November 16, 2007 8
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
November 16, 2007 9
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
November 16, 2007 10
Software AlgorithmDevelopment Process
Algorithms will be 1. Developed in MATLAB2. Tested in SIMULINK3. Converted to C/C++4. Tested in C/C++ model5. Compared to SIMULINK6. Verified on DSP board
November 16, 2007 11
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
November 16, 2007 12
Modularity
Utilities Class
AM ModulationClass
QA ModulationClass
FM ModulationClass
Transceiver
Transmitter Receiver
November 16, 2007 13
Radio Software Design
…
November 16, 2007 14
SIMULINK Model
November 16, 2007 15
Modulation Techniques
• Software Defined Radios allow for multiple modulation techniques
• NO additional hardware is needed– Filtering can also be accomplished
without any additional hardware.
November 16, 2007 16
Amplitude Modulation (AM)
• V(t) = Vocos(2ft + )
– For AM the value Vo is varied to change the amplitude of the signal.
November 16, 2007 17
Frequency Modulation (FM)
• V(t) = Vocos(2ft + )– For FM f is varied.
November 16, 2007 18
Quadrature AM
• V(t) = Vocos(2ft + ) +
Vosin(2ft + )– For QAM, two signals that are out of
phase by 90 degrees are used simultaneously.
November 16, 2007 19
QAM Waveform
November 16, 2007 20
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 typesBPSK, QPSK, …
November 16, 2007 21
Matched Filters
• Maximize the SNR to improve QoS• Receiver filter is matched to the
transmitter filter by the relationship
P R f =C⋅P T f
November 16, 2007 22
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
November 16, 2007 23
Spectrum Digital DSP Boards
SDI TMS320C6713 DSP Boards
• 225 MHz
• 512KB Flash
• 8MB SDRAM
• Microphone, Speaker, Mono In/Out audio ports
• USB Interface
November 16, 2007 24
Demonstration
November 16, 2007 25
Preliminary Testing
MATLAB simulation using AM modulation– Receiver
rectifies signal and detects peaks
Raw Signal
Demodulated Signal
November 16, 2007 26
Any Questions?
November 16, 2007 27
Thank you!
We appreciate your time and thank you for coming!