Students and instructors arriving for class have a lot to think about — that upcoming midterm, what they will cover today, how their hand is going to cramp up as they furiously take notes… one thing they don’t want to worry about is whether they can hear each other or not. Luckily, LSA Technology Services provides microphones in classrooms to aid learning.
However, the COVID-19 pandemic created a wrinkle in LSA Technology Services’ system.
As instructors increasingly needed microphones for lecture capture and to accommodate remote learning, the amount of transmitting radio frequencies essentially doubled. Once it was decided that students could resume in-person learning, LSA Technology Services staff became concerned because the expanded system — containing around 400 microphones — had never been used at full capacity.
With this change, testing the microphones became essential as LSA Technology Services staff prepared for students to return to campus. However, due to a limitation with the microphone manufacturer’s software, there was no way to perform a current system evaluation. The microphones needed to be tested as conflicting frequencies could interfere with each other and disrupt classes. For example, a psychology professor’s lecture could be accidentally broadcasted to the economics course a few classrooms away, or the microphones could just not function at all.
Any additional microphone brought to campus could also interfere with the microphones in LSA spaces. Another U-M college could set up a microphone for an event or a news station could begin broadcasting on the Diag and any nearby classes would be disturbed. With the current system, there was no backup system in place to accommodate real-time interference issues.
A system-wide test was essential but nearly impossible with classes still in session. Kirk Scarbrough, a Project Engineer with LSA Technology Services, developed a method to test the system virtually to avoid disrupting classes.
Utilizing his background in research design, database management, and geographic information systems, Scarbrough was able to assign real world geographic space to each of the wireless channels being used. Then, using the manufacturer's details about range and power, he was able to calculate distances between microphones and ultimately the probability of interference events for each microphone frequency.
By performing this test, Scarbrough identified 32 microphones that were at high or very high risk of interference events caused by other LSA deployed microphones, risking disruption to classes.
A limited practical test in Mason Hall was performed next in hopes of confirming the results of the virtual testing model. In the early morning, 100+ microphone transmitters were powered on and off one by one to observe interference on each microphone receiver. If a transmitter for a room was off but the receiver was seeing a high powered signal, that room was considered to be at risk for interference. All of the predicted high or very high risk rooms showed heavy real-world interference, confirming Scarbrough’s virtual test results.
With students’ return to campus for fall 2021 approaching, it was decided to recoordinate the campus wide system in its entirety. With the help of LSA Technology Services’ Operations staff, all 400+ microphones were visited and each frequency was changed to safely operate within the new coordination. This change not only allows Technology Services to know that all of the microphones that were added during the pandemic are compatible with each other, but also provides backup frequencies for each microphone. LSA Technology Services can now quickly implement pre-designed backup frequencies in the event of interference from microphones from groups outside of LSA.
Since implementation, Scarbrough has monitored the system closely and optimized where applicable. Backup frequencies have continued to be used when needed and have proven to be a reliable method of solving radio frequency issues. Looking forward, Scarbrough is developing methods of predicting areas of campus that are most likely to have interference issues, as well as studying and designing methods to implement new types of microphones to alleviate the complexity of LSA’s current coordination.
