If you’ve used location services on a phone for any length of time, you know they can quickly drain the battery. A Microsoft Research project suggests that there’s a way for location chips inside smartphones to use far less power.
Reducing the power consumption of GPS chips could not only extend the battery life of smartphones and tablets, it could also make it practical to add GPS functionality to more devices, including low-power remote sensors.
The biggest power hog inside a smartphone is the GPS chip. This component can take 30 seconds just to acquire the satellite data necessary to get the information it needs for an initial location fix; it then has to churn through the downloaded codes to calculate its location precisely.
Microsoft researchers reduced that power consumption dramatically by offloading some of the work to the cloud. Jie Liu, a principal researcher at Microsoft Research, and his team developed a GPS system that collects only a few milliseconds of the most crucial information from satellites. This data is then combined with other important information from public, online databases, such as satellite trajectories and Earth elevation values, to calculate the device’s past locations. But the data fusion and location calculations happen on a remote server.
The researchers call the approach cloud-offloaded GPS, and they call the system they built CLEO (Cultivating the Long tail in Environmental Observations). According to research presented last month in Toronto at the SenSys 2012 conference, CLEO can perform continuous GPS sensing for a year and a half efficiently enough to be sustained by just two AA batteries.
In a typical mobile phone, Liu says, continuous GPS sensing would burn through the device’s battery in roughly six hours. (In practice, data from Wi-Fi base stations and cellular towers contribute to location information in mobile phones so GPS doesn’t always do all the heavy lifting.)
CLEO was designed for animal-tracking systems that can acquire movement data over time, and it does not immediately transmit its data to the cloud. But Liu says this approach could be integrated into an Internet capable device, saving power and time when GPS is in use.
Microsoft isn’t alone in trying to make GPS systems more energy-efficient. The Swiss company U-blox has developed GPS chips based on similar principles. Chris Marshall, product manager at U-blox and former chief technology officer of Geotate, a low-power GPS company acquired by U-blox in 2009, says the company’s commercial GPS systems can connect with networks in real time. “The processing could be done either on a server or an Internet-connected PC or tablet, depending on the desired product concept,” says Marshall.
Additionally, researchers at MIT, Duke, and the University of Southern California have all developed signal processing and other engineering tricks to make location services that use GPS faster and ultimately more energy efficient.
Microsoft’s Liu believes that low-power GPS systems on mobile phones could make continuous location logging feasible, which could make the device smarter. You could, for example, opt into a service that contributes to a database of noise pollution levels in your city. Or, if your smartphone kept a record of your driving habits, you might receive tailored directions or search results based on your usual walking or driving directions.
“Those continuous location-sensing applications have a lot of value, and today we’re not doing that,” Liu says.
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