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Only in the hyperventilating startup bubble world can tracking people around a shopping mall with wifi be cooler than tracking your position anywhere on earth w
by drats 14y ago
Only in the hyperventilating startup bubble world can tracking people around a shopping mall with wifi be cooler than tracking your position anywhere on earth with satellites that were put there by huge rockets.
- mortenjorck 14y agoI also get the feeling the author has never heard of differential GPS: http://en.wikipedia.org/wiki/Differential_GPS http://en.wikipedia.org/wiki/Differential_GPS Which actually leads to something I've wondered about before: Why couldn't you (with appropriate FCC clearance) set up GPS transceivers around a shopping mall calibrated to rebroadcast the signal at the appropriate time offset? It would work with everyone's existing hardware and be completely transparent.
- mrsebastian 14y agoDifferential GPS doesn't work indoors, I thought? The main problem is that wireless signals simply aren't reliable. You could "boost" GPS indoors, but that doesn't get around the fact that there are corners, concrete walls, mirrors, humans, and so on. Anyway, we're splitting hairs. The point is that we don't currently have an IPS. It doesn't matter if we extend GPS to work indoors or use other signals to create an IPS -- the point is, we need to create an IPS :)
- joshu 14y agoiirc there are several short-range positioning signals (various flavors of differential GPS, i guess)
- 7952 14y agoGPS is complex and I may be wrong. But for rebroadcast to work the transceiver would need to be placed exactly between the user and the satellite in space; meaning a different location every time the user moves. If not perfectly placed; the radio signal will have travelled further than expected and give the wrong position. I suppose you could attempt to locally recreate GPS signals with multiple transmitters; but this would play havoc with GPS reception outside the building. Why not just use WIFI? Differential GPS is not about rebroadcasting the actual GPS position, but the error from a known position. This allows the device to enumerate the error caused by atmospheric effects.
- modeless 14y agoThe location of each GPS transmitter must be known exactly for the triangulation to work, and existing GPS receivers know nothing about the location of shopping-mall transmitters. They only know about satellites. So that's why you couldn't do this with existing receivers, but I don't know of any reason why you couldn't make new receivers that cooperate with a new type of ground-based transmitter built into cell towers or similar. Multipath might be a problem but it seems surmountable. Do any radio experts here know why nobody has done anything like this for cell phones? (The Wi-Fi/Bluetooth positioning talked about in the article is based solely on signal strength which is far inferior to the GPS method).
- archivator 14y agoI don't think the GPS approach can work with ground stations - what GPS has going for it is line-of-sight to the satellites. Multipath would be a hell of an issue in an urban environment. That said, here's a paper describing various positioning methods - http://emits.esa.int/emits-doc/1-5200-RD25-Signal-processing-techniques-network-aided-positioning.pdf http://emits.esa.int/emits-doc/1-5200-RD25-Signal-processing... EOTD looks rather interesting - https://en.wikipedia.org/wiki/E-OTD https://en.wikipedia.org/wiki/E-OTD
- jf271 14y agoWAAS is a combination of GPS and ground stations. It is accurate to about 6 feet. Widely used in aviation.
- modeless 14y agoThe ground stations don't transmit to your device. WAAS still needs the satellite signals to work and so won't help indoor reception problems.
- toomuchtodo 14y agoCorrect. The ground reference stations multiplex their data to the WAAS satellite, which then pushes the data on WAAS-specific channels (hence, why your GPS receiver specifically needs to be built to support WAAS)