The final laboratory assignment in ECEn 485 (Introduction to Digital Communications) went "over the air" for the first time at the end of Winter Semester 2018. "The availability of inexpensive software defined radios (SDRs) was the enabler here," explained Prof. Michael Rice, the professor who developed and taught the material.
During the semester, students complete a series of laboratory assignments that demonstrate the principles taught in the lecture portion of the class. The laboratory assignments are based on The Mathworks Simulink simulation environment and include exercises in modulation, matched-filter detection, carrier phase synchronization, and symbol timing synchronization. The exercises required students to detect the bits carried by the symbols in samples of a digitally-modulated carrier, then use those bits to find a fun message encoded by those bits.
The culminating laboratory assignment put all the pieces together, but still operated on a file that was posted on the laboratory web page. This year was different. Using the new software defined radios produced by Analog Devices and supported by The Mathworks, a transmitter was set up in the laboratory that transmitted an over-the-air signal. Students shared 12 SDRs to receive the signal and demodulate, synchronize, and detect in real time.
The transmitter produced a 80 kbit/s QPSK signal at 425 MHz. The bits represented two fun messages that were repeated. Using design, development, and debugging skills developed in earlier labs, all the students were able to successfully complete the laboratory assignment.
This laboratory assignment was developed based on two SDRs donated to BYU by The Mathworks. After successfully incorporating these devices in the laboratory assignment, additional radios were purchased for use by the students. All students surveyed felt the final "over-the-air" lab made the concepts and algorithms more "real".