18 Dec 2012

Researchers develop breakthrough WiFi indoor positioning system

US researchers have developed a new method to build a WiFi radio map that does not require GPS signals, but instead relies only on WiFi fingerprints.

For indoor positioning, location-based service providers including mobile device makers have mostly used a combination of GPS and wireless network system such as WiFi, cellular connectivity, Ultra Wide Band (UWB), or Radio-frequency Identification (RFID).

For example, the WiFi Positioning System (WPS) collects both GPS and WiFi signals, and many companies including Google and Apple utilize this technology to provide clients with location information services.

"WPS is helpful to a certain extent, but it is not sufficient because the technology needs GPS signals to tag the location of WiFi fingerprints collected from mobile devices,” says Professor Dong-Soo Han from the Department of Computer Science, The Korea Advanced Institute of Science and Technology (KAIST). “Therefore, even if you are surrounded in rich WiFi signals, they can be useless unless they are accompanied with GPS signals.”

“Our research team tried to solve this problem, and finally we came up with a radio map that is created based on WiFi fingerprints only," he adds.

WiFi fingerprints are a set of WiFi signals captured by a mobile device and the measurements of received WiFi signal strengths (RSSs) from surrounding access points at the device.

Han and colleagues collected WiFi fingerprints from users' smartphones every 30 minutes through the modules embedded in mobile platforms, utilities, or applications and analyzed the characteristics of the collected fingerprints.

A WiFi radio map shows RSSs of WiFi access points (APs) at different locations in a given environment. Therefore, each WiFi fingerprint on the radio map is connected to location information.

"We discovered that mobile devices such as cell phones are not necessarily on the move all the time, meaning that they have locations where they stay for a certain period of time on a regular basis,” explains Han. “If you have a full-time job, then your phone, at least, has a fixed location of home and office."

By taking smartphone users' home and office address as location reference, Han classified fingerprints collected from the phones into two groups: home and office.

He then converted each home and office address into geographic coordinates (with the help of Google's geo-coding) to obtain the location of the collected fingerprints.

The WiFi radio map has both the fingerprints and coordinates whereby the location of the phones can be identified or tracked.

For evaluation, the research team selected four areas in Korea (a mix of commercial and residential locations), collected 7,000 WiFi fingerprints at 400 access points in each area, and created a WiFi radio map, respectively.

The tests, conducted in each area, showed that location accuracy hinges on the volume of data collected, and once the data collection rate hits over 50%, the average error distance is within less than 10m.

Han adds: "Although there seems to be many issues like privacy protection that has to be cleared away before commercializing this technology, it is no doubt that we will face a greater demand for indoor positioning system in the near future. People will eventually want to know where they are indoors just as much as outdoors."

Once the address-based radio map is fully developed for commercial use, identifying locations at the home and office level will be possible.

This opens the door to further applications such as emergency rescue services or indoor location-based services like finding lost cell phones, restaurants, stores, and missing persons, as well as providing information on sales and discount coupons.

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