You've probably noticed that a smartphone finds your location significantly better outdoors than in. It's due to the fact that outside the device can take advantage of a constellation of satellites specifically designed to identify positions, with GPS.
Inside, it's not so easy.
The smartphone has to make do with a patchwork of locating tools, including satellite forecasting, cell towers with databases that know which sector of which base station a phone is using, sensors within the phone to determine direction (such as an accelerometer to tell how fast the phone is moving away from its last fix), and Wi-Fi, among other things.
And it's in positioning via Wi-Fi where some researchers from Spain say that they have made a breakthrough.
The scientists, from networking research organization IMDEA Networks Institute, reckon they have developed a positioning solution that uses software upgrades of commercial, off-the-shelf 802.11 chipsets that can be integrated into any standard Wi-Fi access point.
That would make it a more economical solution for positioning than some ideas, such as terrestrially-located GPS-style transmitters or Bluetooth beacons which have had to be placed every few meters in past trials.
Stephen Lawson of IDG News Service wrote about some of the methods smartphones use for locating in 2012.
Time of Flight
The Madrid-based group's system uses Time-of-Flight (ToF) measurements only and $6 chipsets, IMDEA says in its announcement.
ToF, in this case, is a measurement of the time it takes a radio wave to get from one place to another. In other words, from the access points to the smartphone.
It's a known concept that hasn't always been easy to get right for technical reasons.
The reason the idea is seductive is because if you know the characteristics of the spectrum propagation, along with the time it takes radio waves to get from access points to a smartphone, you can measure the distance and locate the device.
Problems with the idea include reflection, though.
The group says that it has sorted any issues out using software and filters, and that its "pervasive mobile location" system doesn't need any "pre-calibration nor any special hardware," unlike other Indoor Positioning Systems.
It says its filter is novel and "requires just a few samples to estimate the distance range."
And the group says that its system will be very cheap, and that it can be built-out using software upgrades to "commercial off-the-shelf 802.11 chipsets" that can be added to any access point.
Technically, multipath has always been a problem with ToF, however, and for the IMDEA's system to work, they're going to have to sort that out. The team says they have done so.
Multipath is where the radio signals get reflected off objects like walls and furniture, and confound the calculations.
"The system has been tested across different and heterogeneous setups and testbeds, including scenarios with strong indoor multipath, resulting in a median error of the distance of 1.7 to 2.4 meters," the institute says.
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