Real-World Signals in the Lab
RF and communications topics are traditionally taught using a theoretical, math-focused approach in which students derive formulas and build simulations. Many educators see the value of adding a lab component so students can apply the theory with prototype implementations and experiment with live signals, but the opportunity to do so is limited by a lack of affordable, accessible, and relevant tools.
Professor Sachin Katti, head of the Stanford Networked Systems Group (SNSG), removed this limitation from his EE 49 Building Networked Systems course by implementing a new approach with LabVIEW software and NI USRP hardware. Prof. Katti used this educational solution to introduce sophomore-level students to real-time communications signals using software-defined radio.
Building a Complete Communications System
Professor Katti first implemented this approach with a trial group of students in the spring 2011 quarter EE 49 course. With the software/hardware combination of LabVIEW and the NI USRP, students were able to build and explore each element of a complete communications system signal chain. In doing so, the students gained experience with channel coding, modulation, timing recovery, random bit generation, and many other topics associated with a modern digital communication system. Ultimately, the students finished the class by working on a project to complete a link between a transmitter and receiver, a process rarely achieved in an introductory RF and communications course.
In-class experiments gave students hands-on experience with the NI USRP RF transceiver, offering real-time access to a 50 MHz to 2.2 GHz frequency range with an instantaneous bandwidth of up to 20 MHz. The students could immediately see the simple RF on-off keying signals from a standard vehicle remote-controlled keyless entry device as well as an 850 MHz GSM cell phone uplink. They could also analyze the spectrum to find FM radio stations, and even implemented an FM demodulator enabling them to hear live FM radio. In a final class project, each student designed a packet transceiver that returned an acknowledgment signal (ACK) when a packet of data was successfully received and decoded.
Each successive lab encouraged students to implement a specific piece of a communications system. For example, in the fourth lab students studied the concept of demodulation and implemented parts of a wireless binary phase-shift keying (BPSK) receiver for a USRP-to-USRP link. A single transmitter repeatedly transmitted a BPSK packet of information for the students to decode. Each student, with their own computer and NI USRP, developed a receiver to demodulate and decode the signal. The students implemented channel correction, a BPSK symbol de-mapper, a preamble detection scheme, packet decoding, and cyclic redundancy check (CRC) error detecting code over the course of the two-week lab project. The flow of labs allowed students to use the code they developed in a previous lab for packet decoding in the final lab to establish a wireless link.
The response from students in the trial course was overwhelmingly positive, as seen from the following feedback provided by now senior student Michael Duarte.
“It was incredible to actually see how the material we learned in classroom lectures is applied in practice in the lab,” said Duarte. “I was not familiar with the USRP hardware prior to this course, but through understanding and using LabVIEW, I grew very familiar with programming the devices. LabVIEW itself was a pleasure to work with. It was very easy to get things working and debugging was quite simple. Overall, this class was easily my favorite in the three years I have spent at Stanford.”
Students at Stanford were able to easily view and interact with these processes by using the LabVIEW software and NI USRP driver. The LabVIEW development system is ideally suited for signal processing, programming tasks, and hardware interfacing with NI USRP software-defined radio hardware, which enabled the students to develop and explore algorithms for processing received signals and synthesizing signals for transmission.
A New Opportunity for Professors and Students
“We’ve touched on something big here that could revolutionize the way professors introduce students to communications concepts,” said Katti. “Schools across the country have seen a decrease in ECE enrollments, and one reason for this is we’re not always able to give students relevant, hands-on lab experience. This solution helps to solve that very issue.”
Course evaluations affirmed that students were highly engaged in and benefitted greatly from the EE 49 class. “The course evaluations for our class were fantastic,” said Katti. “Students rated the class 4.94/5.0, likely making it one of the highest ratings among all classes in the School of Engineering at Stanford.”
Student comments echoed these strong ratings, with feedback such as:
“Hands down the best EE class I’ve taken so far.”
“Really great for a first-time class…the labs were really helpful for understanding concepts in practice and were interesting in design. I would recommend this [class] to all of my EE friends.”
“Awesome class! I really enjoyed the lectures, and the labs were really cool because we got to use the hardware.”
Because of the success in the trial course, Professor Katti plans to expand the NI USRP and LabVIEW platform to more than 40 students with 20 lab stations for the fall quarter. Katti anticipates this type of course will better prepare students for future signal processing and communications courses. Because of the accessibility of this educational solution, the platform is also applicable to a wide range of other introductory-level signal processing courses, such as information theory and signals and systems. Additionally, the platform scales with the students as they progress in their studies or move on to research or industry applications.
Ultimately, LabVIEW software and the NI USRP hardware provide the affordable, accessible, and relevant solution needed for developing student proficiencies that will make them competitive in pursuing a wireless communications career. Dr. Katti offered to share his course materials with other universities so they also can find ways to engage their students earlier in the curriculum with hands-on experiences in wireless communications.
Please note, the materials for this course will be available on ni.com/courseware this fall.
Dr. Sachin Katti
236 Packard, Stanford University
Stanford, CA 94305