Mostofi "Don't Fidget! WiFi Will Count You"
ECE Professor Yasamin Mostofi and researchers’ new method enables WiFi signals to count a stationary seated crowd, using their natural body fidgets
Researchers in UC Santa Barbara professor Yasamin Mostofi’s lab have enabled, for the first time, counting a stationary seated crowd using WiFi signals, and without relying on people to carry a device. The technique, which also counts through walls, needs only a wireless transmitter and receiver outside the area of interest where the crowd is seated. It has a variety of applications, including smart energy management, controlling the crowd size during a pandemic, business planning and security.
“Our proposed approach makes it possible to estimate the number of seated people in an area from outside,” said Mostofi, a professor of electrical and computer engineering at UCSB. “This approach utilizes only the received power measurements of one WiFi link, does not rely on people to carry a device and works through walls.”
The proposed methodology and experimental results appeared in the recent 19th ACM International Conference on Mobile Systems, Applications, and Services (MobiSys).
In the team’s experiments, one WiFi transmitter and one WiFi receiver (both off-the-shelf) are in an area where a number of people are seated. The transmitter sends a wireless signal whose received power is measured by the receiver. By using only such received signal power measurements, the receiver estimates how many people are present — an estimate that closely matches the actual number.
This innovation builds on previous work in the Mostofi Lab, which has pioneered sensing with everyday radio frequency signals such as WiFi since 2009. For instance, their 2018 paper "Crowd Counting Through Walls Using WiFi" showed how WiFi can count a crowd of mobile people. However, people had to move around to be counted.
“Counting a stationary seated crowd is a considerably challenging problem due to the lack of major body motion,” said Mostofi. Her lab’s success in this endeavor is due to the new proposed methodology they developed.
“While the people in the crowd are stationary, i.e., with no major body motion except breathing, they do not stay still for a long period of time and frequently engage in small in-place natural body motions called fidgets,” Mostofi explained. “For instance, they may adjust their seating position, cross their legs, check their phones, stretch, or cough, among others.”
The researchers have proposed that the aggregate collective natural fidgeting and in-place motions of a seated crowd carry crucial information on the crowd count, and have shown, for the first time, how to extract the aggregate fidgets and count the total number of people based on them.
The researchers then developed a new mathematical model that statistically describes the collective fidgeting behavior of a stationary crowd, i.e., the CFPs and CSPs, and explicitly relates them to the total number of seated people.