Software defined radio based transceiver for educational purposes

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Dr. Horváth Péter
Department of Broadband Infocommunications and Electromagnetic Theory

The reason of this thesis is to implement a project laboratory course for the department, using USRP and LabVIEW Communications. Using this curse material, students will get to know the basics of digital signal processing and radio communications technique. Working on the thesis the main point was to introduce basic techniques to the students that are commonly used in communications systems. Using any programming languages, the covered algorithms are already existing functions that are maybe stay hidden from the user, so its' deeper understanding would not be possible. To show the usage of the theoretical knowledge taught at the university I have recreated these functions from scratch, so the student would be able to see how these algorithms working in a real life environment.

The thesis covers a simplex communication system that has pseudo-random bit generation, forward error correction, coding, modulation and many other functions implemented. The designed system first generates random data. To achieve this, I have implemented a linear-feedback shift register. The generated noise like signal will represent the message to be sent. The generated message then goes under cyclic redundancy check and channel coding. The channel coder is in this thesis is a convolutional coder. After, guard and synchronization symbols the added to the coded bits, which adds up a burst. The burst then goes under the modulation process (DBPSK) and ready to be upconverted by the software radio for transmission.

The receiver side does a quite similar but mirrored process as the transmitter. After down converting and demodulating the signal, the synchronization bits are searched, and the received messages are stored. These messages are decoded and sent through the CRC function. The restored message and acquired waveform then able goes under some measurements. These are BER, BLER measurements, CRC check, spectral measurements, eye and constellation diagrams and other similar measurements and visualizations.

Making it able for the student to concentrate on the DSP algorithms and techniques the user hardware and simulation framework is already provided. Students will need finish blocks, functions by their own and should answer some questions regarding some more complex processes, that are more advanced to implement. The thesis introduces these techniques for the students and covers a set of instructions step-by-step and questions to be answered. During their semester they will create a working communication system that they are able to test modularly and run it on a real hardware.


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