The Global Positioning System (GPS), the satellite-based navigational system, has transformed how maps are made and the way the world gets around in the great outdoors. Its biggest weakness: the indoors.
Some Microsoft researchers are working to help bring GPS-enabled mapping and location services past the front door.
"While Earth's outdoors environment has been mapped extensively, indoor localization of places such as shopping malls or department stores remains an elusive dream," observed Inside Microsoft Research author Rob Knies in a blog post. Jie Liu, principal researcher and a research manager in the software giant's R&D unit, is working with a group to turn it into a reality.
A paper from Liu and his colleagues, titled "COIN-GPS: Indoor Localization from Direct GPS Receiving," describes how GPS equipment, a specialized antenna design and cloud computing can combine to extend GPS to indoor spaces.
"People spend more than 80 percent of their time indoors," stated Liu in the post. "Location is key contextual information to enable smart services, such as Cortana."
Cortana is Microsoft's voice-enabled digital assistant technology for Windows Phone 8.1. As the company's answer to rival solutions such as Apple's Siri and Google Now, Cortana can be enlisted to manage contacts, juggle calendars and configure alerts including location-based reminders.
To enable granular location services that work seamlessly between both indoor and outdoor locations, Liu's team decided to push the limits of GPS signal processing.
The researchers' solution involves "using a steerable, high gain directional antenna as the front-end of a GPS receiver along with a robust signal processing step and a novel location estimation technique to achieve direct GPS-based indoor localization," according to an abstract published by Microsoft. "By leveraging the computing power of the cloud, we accommodate longer signals for acquisition, and remove the requirement of decoding timestamps or ephemeris data from GPS signals."
In a test of 31 random indoor, single-story locations, the team was "able to obtain location fixes in 20 of them, with a median error of fewer than 10 meters," wrote Knies. "This is a scenario in which all normal GPS receivers fail."
Why not WiFi? Liu explain that current methods of profiling indoor spaces using the wireless networking technology "is a time-consuming and expensive process, because there is no ground truth to 'nail down' the Wi-Fi maps." It's also a high-maintenance endeavor, since the number and locations of WiFi access points can vary as time passes.
It may take time for the technology to see the light of day, however. In its current state, the solution's antenna array consists of 16 antennas on a 10-by-10-inch board.
Indoor mapping has attracted the attention of tech companies as they race to quantify the physical world. In March 2013, Apple snapped up WiFiSLAM, an indoor location services startup, reportedly for $20 million. Aruba Networks followed suit in May of the same year by paying an undisclosed amount to acquire Meridian Apps, a maker of navigation software for public venues.