Forget GPS, Hello WPS 286
No France writes "A company known as skyhook wireless has announced the commercial availability of its Wi-Fi Positioning System, or WPS. The company has compiled a database of every wireless access point it can find in a given city. When a mobile user running th Skyhook client is in a recorded area, their position is calculated by selecting the surrounding signals and comparing them to the reference database. Currently there are 25 US cities mapped, including New York City, Boston, Chicago, Los Angeles and San Francisco. Apparently this device is accurate to within 20-40 meters, though one has to wonder how well it deals with people moving their wireless access points."
Been there, done that! (Score:5, Informative)
You've never been to Japan I see! (Score:3, Informative)
GPS SA off since may 1, 2000 (Score:4, Informative)
Basically, the military figured out how to easily jam GPS in an area. But before then, there were GPS field units available that averaged out the error and got better than 2-3 meters so that it didn't really matter that much...
Re:20-40 meters? (Score:3, Informative)
GPS has come down in price incredibly in the last few years. You don't even need a subscription to a DGPS service anymore.
Re:Useless? (Score:1, Informative)
Re:What a joke... (Score:5, Informative)
Sub-meter accuracy: A little bit of position averaging + basic DGPS makes this easy for a stationary receiver, even when SA was on DGPS could cure the intentionally added errors. Very difficult to use with a moving receiver unless combined with an inertial navigation system. (Rare except in modern airplane navigational systems)
Millimeter accuracy: Also possible before SA was turned off, but required the receiver to be stationary for a long period of time, and required significant postprocessing of the data using a variant of DGPS. It still requires stationary receivers for nonmilitary systems.
About the only thing that can't be done without a method for decrypting the P code is sub-centimeter positioning of a moving object. Even with the P code available it can't be done without combining a high-grade inertial navigation system with the GPS system.
Re:Been there, done that! (Score:5, Informative)
Re:Been there, done that! (Score:3, Informative)
I see what you're saying though, that a moving GPS on a single wardrive will have some error based on atmospheric effects, but repeated resurveys of an area on different days would tend to average these out, similar to the long-term averaging of a stationary GPS receiver.
My point was that the spokesdude in the article is either misquoted or misinformed about the accuracy of GPS, and that the neither Skyhook nor PlaceLab is likely to return better outdoor results than a consumer GPS receiver. Indoors is where this concept really shines.
Re:Been there, done that! (Score:2, Informative)
Re:What a joke... (Score:5, Informative)
I would imagine that supplementing GPS with other position determining mechanisms (like WiFi) could be beneficial in these circumstances.
Ekahau did this as well, but better. (Score:4, Informative)
The client software running on the tracked device measures the signal strength of the access points, forwards the data to the server which calculates the position. The big-brother scenario is avoided as long as you still have to install the client yourself.
The major drawback of the system is that it needs extensive calibration, since they are using not only the available access points, but also the signal strength of these. Normally they suggest calibration in a 5x5m (15x15ft) grid. More calibration points yield a more accurate result.
And now the piece of information you have all been waiting for: accuracy. With a good calibration this can yield accuracies of arround 1m. In my tests (indoor) the accuracies fluctuate a bit, but is at least better than 3m 95% of the time.
Just as the system described in the original post, Ekahau requires no extra hardware (we already have 2-300 APs on campus).
That's not a security measure... (Score:2, Informative)
What manual says to do this? Turning off SSID broadcast is *not* a security measure in any sense, at all.
For one thing, the SSID is included in every single packet that the access point sends out. Period. So getting it is easy with or without the SSID broadcast.
For another thing, turning off SSID doesn't prevent anybody from connecting to the network. It will prevent stupider displays like Windows's wireless page from showing that access point as available, assuming no other AP has the same SSID being broadcast, but if they select that SSID from another AP or if they put it in manually, then they'll connect to your network just fine.
If you want security, enable WPA. Turning off SSID, filtering by MAC address, these are not security related adjustments, and add precisely nothing to your overall security strategy. They might be a way to keep your idiot neighbor from connecting to your network by accident, but they won't keep anybody from connecting to your network on purpose.
Re:20 - 40 meters? (Score:2, Informative)
> Where am I?
You do know that access points have MAC addresses, don't you? Every single MAC address is globally unique. They have a database of those, _not_ of the names.
Note that this database is going to get stale quickly, as people turn on new APs, move existing ones, or upgrade broken ones. Still, I think it's a great thing to keep in your arsenal of positioning tools.
Re:20 - 40 meters? (Score:2, Informative)