1. Software Defined Radio
A Modular Approach
November 16, 2007

2. What is SDR? Software Defined Radio Precursor to “Cognitive 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
Talk about software radio and what it is and isn’t.
SDR is:
Smart algorithms designed to work at various bands in the radio frequency spectrum
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
Basic overview of the history of radios
Mention other SDR groups
November 16, 2007

4. 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
Define the problem.
Is this enough detail?
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)‏
Describe our basic game plan. We want to elaborate here more.
November 16, 2007

6. Block Diagram of a SDR November 16, 2007
Block diagram of a good SDR system. The key to this is where the sampling takes place – right after the LNA. A good software radio will have the ADC/DAC as close to the antenna as possible. This allows all the processing of the signal to take place in software. Everything outlined in red will be part of the software system. The actual transmission and reception of signals, the LNA/AGC functionality, and the sampler are taken care of in hardware.
November 16, 2007

7. Transmitter Coder Block Bit/Symbol Transmit Filter Modulator
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
Tx detail.
November 16, 2007

8. Channel Channel properties White Noise Interference
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
Channel detail.
November 16, 2007

9. Receiver LNA/AGC Sampler Demodulator Carrier Recovery Matched Filter
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
Rx detail.
November 16, 2007

10. Software Algorithm Development 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
November 16, 2007

11. 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++
Linux
Documentation
Cross-Platform
Macintosh and IBM Compatible
Matlab code is very similar to C. Using C++ will give us the ability to convert from C easily while adding the modularity of classes.
November 16, 2007

12. Modularity Utilities Class AM Modulation Class FM Modulation Class
QA Modulation
Class
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) = Vocos(2ft + )‏
For AM the value Vo is varied to change the amplitude of the signal.
November 16, 2007

17. Frequency Modulation (FM)
V(t) = Vocos(2ft + )‏
For FM f is varied.
November 16, 2007

18. 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.
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 types
BPSK, QPSK, …
November 16, 2007

21. Matched Filters Maximize the SNR to improve QoS
Receiver filter is matched to the transmitter filter by the relationship
Maximizing the SNR will improve QoS because the signal power will be accentuated while the noise power will not. This allows for better decision making in the data-aided timing recovery algorithms.
Matched filter – P_x(f) is the FT of the filter. C is a constant. An adaptive MF allows for C to change and converge to the ideal solution (with minimal delay).
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
A combination of both provides very accurate results. Non-data aided in acquisition, data-aided in 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
Demo diagram – next slides explain more.
November 16, 2007

25. Preliminary Testing MATLAB simulation using AM modulation
Receiver rectifies signal and detects peaks
Include scope output and Simulink block diagram here.
Raw Signal
Demodulated Signal
November 16, 2007

26. Any Questions?
November 16, 2007

27. We appreciate your time and thank you for coming!
November 16, 2007