Exploring Modular Design of SDR Transceivers Course
The first course of the series, Exploring Modular Design of SDR Transceivers, was introduced in spring 2012. This course focuses mostly on digital transmission algorithms and techniques and introduces the NI USRP SDR platform to students. It gives students a solid background to advance to a second course the following semester that introduces MAC-layer and packet radio principles and algorithms. The educational plan includes the two semesters for students to master the basics of modern digital communications-based packet radio networks. It also has the goal of instilling basic transmitter and receiver design knowledge so students can ultimately implement and test network protocols and algorithms on hardware over a real wireless channel.
The first course was launched as a novel hybrid course that efficiently mixes theoretical lectures and practical laboratories using NI tools. This provided students a unique opportunity to design and test real communications systems and integrate knowledge from different courses.
Making SDR More Available to Students
Communications engineering is one of the specialization fields electrical engineering students can choose at RWTH Aachen University. Digital communications and systems are topics that students first discuss during the second year of their communication engineering studies. In most cases, the concepts are taught through theoretical lectures supported by mostly disjointed laboratory courses on selected digital signal processing (DSP) themes. Due to a lack of affordable hardware and relevant tools, the labs usually enable students to only simulate communication systems and their components but not build, experiment, and test with real configurable radio platforms.
The comprehensive mastery of systems engineering has also become an important topic, and the wireless industry has encouraged us to prepare students better to understand implementation issues related to systems. SDR techniques supported by a powerful graphical system design approach enabled by LabVIEW software provide an opportunity for the students to gain such knowledge and experience, even with the limited time and budget that many professors face.
Pilot Course: Building and Testing a Complete Single Carrier Communication System
The main goal of the course is an integrative one: to make the connection between the theory of digital communication systems and practical implementation as well as test the students’ own designs. The students were given a critical education experience using the NI USRP SDR platform to solve problems in communication systems design that they would have never anticipated through theory alone. The combination of NI USRP boards and LabVIEW offers a complete platform students can use to send and receive actual signals over a real wireless channel and explore and experiment with algorithms for channel estimation, equalization, and symbol and frame synchronization without worrying about hardware-specific implementation issues.
During the 12-week course, five sessions were dedicated to refreshing the students on DSP theoretical concepts in digital transceiver design, including introduction to SDR concepts. In the remaining sessions, students could focus on practical design, implementation, and testing their own communication system modules using LabVIEW and the NI USRP boards. Interchanging theory and practice at the beginning of the semester on a weekly basis was extremely effective for the students and kept them fully engaged and focused on their designs by having both the required theory background and the hardware platforms at hand.
“We chose an approach where students had to develop their own modules, modify existing modules, and integrate them all together,” said Dr. Petrova. “This approach not only kept the complexity of the course work at a reasonable level, but it also simulated the industrial R&D environment where many students will work after obtaining their degrees.”
To use most of the time in the lab for experimenting with their designs, students were given homework assignments for each hands-on session and were encouraged to test their ideas using the LabVIEW simulator first. In the class, the students were provided with a pair of NI USRP transmitter and receiver boards with a tunable carrier frequency between 50 MHz and 2.2 GHz and could use up to 20 MHz bandwidth. With this setup, the students easily realized the physical layer of the complete single carrier transceiver and tuned its parameters to achieve optimized signal reception, thanks to the reconfigurability of the SDR platform.
The progress toward a complete system design and learning trade-offs between different solutions was gradual. Each hands-on session allowed students to master a single component in the transceiver chain. In the third session, for example, the students could build and test a BPSK and QPSK modulator and demodulator including the necessary components such as pulse shaping and matched filter. Furthermore, students studied and implemented symbol, frequency, and frame synchronization; least square channel estimation; linear channel equalization; and finally, channel error detection and correction codes. By the last session, students could integrate all the components and experiment with the complete design.
Encouraging Feedback and Next Steps
The reaction and feedback from the students participating in the first pilot class was positive. They enjoyed the opportunity to get their “hands dirty” and play with actual tools that helped them design their first radio systems. The students expressed their enthusiasm by giving not only high ratings to the course but also a lot of direct feedback, such as the following:
“All the theoretical things I learned in the course were more or less the same that I have been studying for a long time in communication engineering. But the way these things were presented in the course, with the very practical implementation, really helped a lot in visualizing how things actually work. This has cleared a lot of ‘ifs’ and ‘buts’ that used to be in my mind regarding communication systems, and at the end of this course, I happened to be a more refined individual in communication systems.”
Another student provided the following feedback: “I would like thank the whole team for offering such a sublime course that helped us envision and groom ourselves in the communication engineering field…”
Encouraged by the excellent experience with the pilot course in spring 2012, including the excitement and the positive feedback from the students, I plan to establish the course permanently in the faculty curricula. I teamed up with Dr. Mähönen, head of the iNETS Research Group to introduce the second companion course. In this course, the students will use their earlier designs as a starting point and learn how to implement full packet radio systems including the implementation of medium access control and cooperative communications algorithms.
Institute for Networked Systems RWTH Aachen University