Mobile software blends Wi-Fi/GPS signal for accuracy

Skyhook Wireless upgrades mobile wireless package

Skyhook Wireless has released the latest version of its positioning software, adding new algorithms to blend Wi-Fi and GPS signal data to boost accuracy data, and using cellular signals as a new option for mobile devices to fix their location.

XPS 2.0 will give customers a choice, and blend, of three positioning options: Skyhook's original Wi-Fi Positioning System (WPS), GPS, and now cellular base stations. Apple liked the original version enough to include it as a standard element in its iPhone.

The Skyhook software is sold to device makers and mobile carriers to load as firmware onto mobile devices. The code exploits a handset's existing radios, and when available, the satellite GPS interface. In the original version, which impressed Network World blogger Craig Mathias, the software checked for Wi-Fi signals, compared them with Skyhook's database of millions of access point locations, checked the GPS data, and then selected the one deemed most accurate. In dense urban areas or indoors, that would often be the Wi-Fi fix.

The new version makes two key changes. First, it now collects the raw signal data from both Wi-Fi access points and any available GPS satellites, and runs them through a set of algorithms to calculate the best possible fix based on data from both, says Ted Morgan, CEO and cofounder of Skyhook. Second, if those radio sources are not available, the software can make use of cellular signals to give an almost immediate, but much less precise, fix.

GPS is very precise, and a rash of specialized location products increasingly smarter versions of it.

But GPS requires that a device be able to pick up signals from at least three satellites to calculate its location, according to Morgan. In some cases, that may not be possible; in other cases it may take 30 to 60 seconds to complete, compared with less than 5 seconds for the Wi-Fi positioning. Running tests in an "urban canyon" created by adjacent tall buildings in Boston, Skyhook found that the handsets could get a standard GPS fix 70 per cent of the time.

XPS 2.0 can start processing data almost at once, from both the Wi-Fi Positioning System (WPS) and the satellites. "We use the data from just two satellites, and then blend this with our WPS data to improve the latter's accuracy quickly, and then shut everything [saving battery power]," Morgan says.

Skyhook says the new version improves accuracy by a range of 35 per cent to 50 per cent. That means if you previously got an indoor fix with 50-meter accuracy, you now can get a fix with 30-meter accuracy, Morgan says.

As it did with Wi-Fi access points, Skyhook has launched an ambitious cell tower mapping effort, starting in metropolitan areas. Using signal tracking gear, drivers systematically cruise an area, picking up cellular signals and fixing their locations, and then adding the locations to an ever-expanding database. If WPS and GPS aren't available, the cell tower positioning data can quickly yield a more approximate fix within a 300- to 400-meter range.

XPS 2.0 is now shipping for device makers and mobile operators.

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John Cox

Network World

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