Navigating the Great Indoors

The smartphone industry is gearing up to get you around when out of sight of GPS satellites

Image: STMicroelectronics

Inside Out: STMicroelectronics and others want smartphones to get you around in malls and other indoor spaces.

Google, dumped by Apple as the iPhone’s default navigation app, is doing more than chortling at Apple’s well-documented mapping troubles. It’s fighting back with more navigation features, many likely intended for use indoors. And a number of major mobile device makers and cellphone service providers have teamed up to develop a standard for indoor navigation, an effort that neither Google nor Apple is part of. 


Indoor navigation technology is going to be quite a bit different from its outdoor counterpart. Outdoors, navigation relies for the most part on GPS, whose accuracy ranges from 1 to 10 meters. Indoors, because of attenuation and scattering, GPS falls apart. And even outdoors, GPS is vertically challenged; it’s about one-third as accurate at pinpointing your elevation as it is at telling where you are on the ground. In other words, even if you do get a signal inside, it’s unlikely that GPS will have any idea whether you’re trying to navigate the first, second, or third floor of your local shopping mall. 


So indoor navigation, while relying on GPS to identify your general location (at the mall, at the airport), needs some other technology to get you around. Google’s My Location technology uses nearby cellphone towers for identification when GPS is not available. Although cellphone signal triangulation offers some help indoors, it’s not very precise. So increasingly, indoor navigation systems like My Location are supplementing cellular signals with information from Wi-Fi hot spots. It will, however, take time to map venues with information about the comparative strength of Wi-Fi signals at different points. Some proposals would add locator beams that use Bluetooth, WiMax, or other radio standards around indoor venues to help update or correct the system’s understanding of your location.


Still, even with all those radio signals, knowing exactly where a mobile phone user is standing in a crowded mall is tricky. So developers are starting to incorporate information from sensors within the phone, like gyroscopes that determine direction, accelerometers that count steps, and even atmospheric pressure sensors to provide an estimate of altitude.


Benedetto Vigna, executive vice president and general manager of the analog MEMS and sensors group at STMicroelectronics, says that the sensor plus radio approach, in which you “basically trust the sensors in the system and once in a while check in with a wireless signal” is the way to go, because it reduces power consumption compared with an approach that relies on constant radio signal access. Mike Stanley, a systems engineer at Freescale Semiconductor, agrees. It may not seem like much, he says, but “powering up a radio once a second instead of constantly stretches battery life.” Of course, both companies make the MEMS sensors needed for such navigation, so they have a stake in such a scheme’s success. But considering the minuscule electrical requirements for, say, a 3-axis gyroscope—about 6 milliamps—it’s a good argument. 


While this sounds like a lot of technology to throw at something that’s needed only occasionally, the good news is that most of today’s smartphones already come fully loaded with much of the necessary hardware. The Samsung Galaxy S III, Vigna says, has all the sensors, and most other phones are just missing the pressure sensors. So, for the most part, it’s just a question of getting the software to the phones and collecting additional data, like the location of Wi-Fi hot spots, from indoor venues. 


Of course, it would help if these systems were standardized, so that folks with iPhones could go to the same malls as folks with Androids. But while real standardization is not likely anytime soon, indoor navigation is indeed arriving. “I had expected a boom in 2013 or 2014,” says Stanley, “but it is happening already.”

Portions of this article appeared in IEEE Spectrum’s Tech Talk blog in September.

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