Introducing Digital Data Transmission to Students With the NI Software Defined Radio Platform

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"We chose NI tools to equip our research labs with the latest technologies for innovation and discovery and further use these tools to enable students of all ages to learn and understand basic communications concepts."

- Jan Dohl, Technische Universität Dresden

The Challenge:
Introducing seventh- and eighth-grade students to the fundamentals of digital data transmission using radio waves as part of a technology-exploration program involving students from Martin-Andersen-Nexö Gymnasium School in Dresden, Germany.

The Solution:
Using an accessible software defined radio platform with an intuitive graphical programming approach so that young students can explore and understand relatively complex topics in radio frequency (RF) and communications theory.

Author(s):
Jan Dohl - Technische Universität Dresden

University and High School Partnership

Emphasizing its special focus on natural sciences and mathematics, Martin-Andersen-Nexö Gymnasium School has partnered with Technische Universität Dresden to provide students with early insight into real research activities. In the one-week program, students work in small groups to conduct three days of hands-on research. Research tasks are designed so the students can explore the topic on their own as much as possible. The advisers give only hints and intervene if the students veer too far off the right track. On the fourth day, students prepare a poster and a presentation to share the results with classmates, teachers, and parents on the fifth day. The strict time limit of the presentations is especially important because it requires the students to focus on the most imperative results. The group advisers intervene even less during the preparation of the posters and presentations.

The Vodafone Chair at Technische Universität Dresden offered a lab project for the students that dealt with digital data transmission using radio waves. In 2012, three students from the seventh grade chose this lab project. Because students are unfamiliar with both the physical and mathematical concepts of radio waves, the project started with an introductory presentation on the following topics:

  • Short historical breakdown of radio communications
  • Basic properties of radio waves (amplitude, frequency)
  • Radio channel (path loss)
  • Digital data transmission using two distinguishable states (for example, high and low frequencies)
  • Introduction to Morse code

Morse code, also known as code-width modulation, was chosen for data transmission since it is simple, translates directly to letters, and can be “read” by looking at the signal waveform.

Making Complex Theory Intuitive

Although there is an increasing interest and demand in wireless communications and RF-related engineering, there are few to no educational resources available to help young students learn and understand the associated complex theory. We chose NI tools to equip our research labs with the latest technologies for innovation and discovery and used them so that students of all ages could learn and understand basic communications concepts.

With NI LabVIEW graphical programming software and the NI USRP software defined radio platform, students can test their ideas with real-world RF signals, change parameters in real time, and see the results of their work. This provides much needed practical experience for our engineers who will be meeting real-world engineering challenges in the future. With NI tools, complex mathematics can become simple and intuitive.

Providing Hands-On Exploration

With the goal of teaching a young set of students with this weeklong lab project, the week was split into two core research topics. The first topic was wave propagation and path loss. The goal of this first experiment was to explore the various influences on the signal power of a received radio signal transmission. The equipment for the experiment consisted of two NI USRP-2920 radio transceivers and two computers. The transmitter was stationary, while the receiver antenna was mounted on a movable tripod.

The experiment consisted of three stages. In the first stage, the students were asked to find out what was affecting the received power level. At this point, we had not given the students any hints and allowed them to embark on experimenting without supervision. Thus, the students could get acquainted with the equipment and make their hypotheses about how and why radio waves are affected by the environment. They were tasked with specifically observing how the distance between the antennas, the antenna polarization, and the reflection from walls and metallic obstacles act as major factors affecting the path loss.

In the second stage, the students were asked to quantify the dependency between antenna distance and path loss with scientific measurements. Again, we tried to intervene with the planning and measurements as little as possible. In the third stage, we explained the meaning of the path loss exponent to the students and how it is defined mathematically. Then, the students were asked to estimate the path loss exponent from their measurements. The goal of this task was to show that some useful information that characterizes the radio channel in general could be extracted from their measurements. The students solved these tasks with only minor hints from the mentors within the first day. The LabVIEW GUI we provided for the experiments was perceived as easy to understand.

The second research topic involved performing digital communications using Morse code. The goal of the second experiment was to explore and ultimately build a radio receiver for Morse code from the given components. The following receiver blocks based on LabVIEW were provided for this task:

  • USRP initialization
  • Signal capturing
  • Energy detection
  • Frequency demodulator
  • Signal quantization
  • Clock recovery
  • Morse decoder
  • Morse code-to-text converter

The students were given a lab manual with a short description of each receiver component as well as the received Morse code signals captured by the USRP receiver radio. Each component was provided as a LabVIEW VI with a GUI that displays details about the inner workings and several parameters that needed to be adjusted. The result of this experiment was to assemble the blocks in the correct order to generate a working LabVIEW program featuring all receiver components in the right order with appropriately adjusted parameters. This program was then able to decode a “secret message” that was transmitted wirelessly and captured by the receiver with the NI USRP hardware.

The final part of this experiment was to test the performance of the receiver. The students added artificial noise to the signal to learn at what noise level the receiver could no longer receive the secret message correctly. By repeating this measurement for different received power levels, the signal-to-noise ratio (SNR) was estimated, which is one of the most important quantities in data communications.

Conducting a Successful Lab Project With LabVIEW and NI USRP

We offered this lab project for the first time in 2012, and it was a success. The students were able to pick up the concepts of wireless communications very easily and impressed us by solving the tasks much faster than expected. The feedback we received was positive as well. The students liked the approach of exploring the topic and working on their own with just some discussions about the results and next steps in between. Students appreciated the opportunity to work with real radio waves, and, at times, were challenged by unexpected results, a critical component to understanding the RF and communications concepts in real-world systems.

LabVIEW and NI USRP composed the accessible platform that not only ensured this project’s success but also helped us create, document, and facilitate the project in an extremely short timeframe. All required development work was done in less than one week, including the design of all the GUIs. The NI USRP software defined radio platform is an effective tool to teach communications concepts to students, and we look forward to offering the lab project again next year.

Author Information:
Jan Dohl
Technische Universität Dresden
jan.dohl@ifn.et.tu-dresden.de

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