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Wireless Positioning
An anonymous reader writes "This Intel-written whitepaper introduces a way to determine location with the aid of freely accessible, nearby radio sources, such as fixed Bluetooth devices, 802.11 access points, and GSM cell towers. Basically, the device reads the IDs of these local 'radio beacons' (each of which has a unique or semi-unique ID), looks up their positions in a locally-cached database, and performs a computation akin to triangulation. Intel created Place Lab in an effort to satisfy the emerging requirement for location-awareness within mobile devices such as smartphones, PDAs, and laptops, or even moving vehicles. According to the whitepaper, over four million of the required radio beacons have already been mapped."
Sounds interesting. As geeky teens we tried making our own positioning system using 3 transmitters, one receiver and a PC. It never worked well as we didn't know how to properly encode the current time into the 'pings' to calculate the transit time.
Do all these broadcast cells broadcast the time code? Are the clocks in sync or do they need to be? I'm guessing without a way to "time" pings received, there's no easy way to validate your position.
The "need" to find yourself seems sort of a waste for most. GPS is nice but I'm more interested in real time user voting on traffic (on their road, in their direction). GPS + realtime traffic heuristics could offer faster escape routes during evacuations, or better gas mileage by avoiding idle periods.
I am no expert, but I think the reason they have GPS is this: Some cell phones use a time modulation technique to fit multiple users on a small frequency range that was allotted to them. This technique involves shifting parts of your signal in the sub-microsecond range (I dont actually know how fast the shifts occur), and as such require very precise timing (if not the tower and phone would not be in sync I suppse). GPS is the most logical way to achieve this, as GPS sat's transmit the current time as well (each GPS sat has an atomic clock on board). So, they use GPS to get extremely accurate times, which are then used for what I can only describe as their 'ninja-foo' signal manipulation to fit many users in a rather limited frequency space.
Why can't the beacon devices themselves use this method to locate themselves relative to each other? Add a protocol for exchanging this information, and whatever devices are in the neighborhood could quickly reach a consensus as to their relative positions. And if one or more of them are GPS-enabled, voila, we have automagical mapping.
This idea was used in at least one Vernor Vinge story, "Fast Times at Fairmont High". The protagonists dropped wireless routers as "breadcrumbs" and after about four were down, they could accurately identify their position (relative to the routers).