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Locate your friends in a crowd of strangers
 (+4, -1) [vote for, against]

Have you ever lost your friends in a rock festival and having to spend the rest of the evening with a bunch of beardy nutters from the English West Country. If you have you will know that it is a lonely and frightening experience.

The Bluetooth (R) Buddy Radar could ensure that this scenario never happens again.

Imagine:

1. A group of 3 or more drinking-buddies huddle together to synchronise their radar application.

2. Said group disperses - some goes to the bar, some to the latrines - you know the scene.

3. Each phone in turn fires a pulse of Bluetooth signal which contains a precise time-stamp, and each phone notes the time each signal took to arrive.

4. Each phone then transmits this this information to the other phones and a simple algorithm could work out where each phone is in relation to each other. The positions could be displayed James Bond-style on the phones' screens.

I realise that mobile bluetooth devices have a very limited range, therefore I propose extending its reach thus:

Some other, unknown, people in the crowd also has this application installed on their phones. Our signal could be relayed through their devices and theirs through ours. The stranger's radar application need not be synchronised with ours as long as the time-stamp signal is adjusted to compensate for the gap between receiving and re-transmitting.

 — 7ennyn, May 30 2006

GPS in the wikipedia http://en.wikipedia.org/wiki/Gps
[st3f, May 30 2006]

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...or just call the phone they're already carrying...
 — epicproblem, May 30 2006

 So you want to do local GPS, somehting that is done with thousands of dollars of equipment with fast processors and a dedicated radio band on a small, cheap device with a slow processor and have it try to do the same work on a packet-based shared frequency while keeping the hardware running as a mobile phone. Sounds like a 'me to'. "I'd like this expensive thing on my cheap mobile phone."

Have you looked at the technology to see if this is possible?
 — st3f, May 30 2006

[st3f] - No, I haven't looked at the technology in any great detail (or in any detail!) - I have less than a vague idea of how BT works. This is why this is posted in the Halfbakery rather than the Patent Office. However, the trilateration calculations shouldn't tax the phone's puny processor much. But I don't expect this system would achieve anything close to pin-point accuracy.
 — 7ennyn, May 30 2006

The trouble I see it is not the maths but the timings. You're dealing with radio which travels at the speed of light (ish). If you can time a signal to 0.1 milliseconds you can measure a distance to within about 30 kilometers. GPS has some clever tricks to avoid having to time signals directly. [link]
 — st3f, May 30 2006

 You perhaps simplify this: just ping your buddies within in range, they would then share their buddy-list back to you (extending your range) and so on; you could then get an approximate idea of how far away people were from the group.

 (Each radius is 10m at the moment with bluetooth I believe)

(+)
 — monojohnny, May 31 2006

 ie. you measure the distance between buddies in 10m 'hops'.

 1 hop=within 10m 2 hops=within 20m

etc
 — monojohnny, May 31 2006

 in fact it could work a bit like DNS -

 "Can I find user?" , if no then ask a nearer node to ask......

 I reckon this could work.

In fact you could probably write it in Java (which has a bluetooth API) for a Symbian (or other) phone...
 — monojohnny, May 31 2006

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