How Do You Count People Using Wi-Fi?

Other than providing wireless communication facilities, Wi-Fi can have other uses as well. Researchers at the UCSB are now experimenting with a common wireless signal to tell them the number of people present in a designated space. Astonishingly, these people need not be carrying any personal devices on them.

At Professor Yasamin Mostofi’s lab in the UC, Santa Barbara, researchers are demonstrating that wireless signals have more uses than simply providing access to the Internet. With a Wi-Fi signal, they are counting the number of people in a given space. According to the researchers, this technology can lead to diverse applications, such as search-and-rescue operations and energy efficiency.

Mostofi explains the process as estimating the number of people walking about in an area, based on the scattering and received power measurements of a Wi-Fi link. Moreover, it is unnecessary for the people being counted to carry any Wi-Fi enabled telecommunications devices.

In the demonstration, the researchers placed two Wi-Fi cards at the opposite sides of a target area measuring roughly 70-square-meters. They measured the received power of the link between the two cards, and this approach allowed them to estimate the number of people walking about in that area. So far, they have been successful in detecting up to nine people in both outdoor and indoor settings. Mostofi’s research group will be publishing their findings in the special issue on location-awareness for radios and networks in the Selected Areas in Communication of the publication of the Institute of Electrical and Electronics Engineers Journal.

According to Mostofi, the main motivation for this work comes from counting several continuously walking people in a small area by measuring only the power of one link of the Wi-Fi signal.

The researchers count people relying to a large extent on the changes in the received wireless signal. Human bodies scatter wireless signal, and when a person crosses the direct wireless link between the two cards, there is a distinct attenuation of the signal—both effects combining to form multi-path fading. Based on these two key phenomena, and a probabilistic mathematical framework, the researchers have proposed a method of estimating the number of people walking in the space.

With Wi-Fi abounding in most urban settings, the researchers estimate a huge potential for their findings for many diverse applications. For instance, smart homes and buildings can estimate the heating and air-conditioning requirements based on occupancy or the number of people present in a given space at the time. Stores can go for better business planning based on the number of shoppers on specific days of the week.

Occupancy estimation could also help in security and rescue operations. Remote estimation of the number of people stranded at a place can help with the organization and logistics involved in arrangement of the transportation required to rescue them. Mostofi and his team have also done extensive research work in their lab involving estimation of stationary objects and humans through walls using Wi-Fi signals. They ultimately plan to bring the two projects together in the future, so that security and rescue operations can commence with better preparation.