Electronics > Electronics

Precise Distance Sensor - No Line of Sight


I'm wondering what the best approach for this is.  I'm looking for a distance sensor to readout the precise distance within a few inches of a beacon or sensor without line of sight.  For example, if I were to give my friend the sensor(in his pocket) in a crowded mall and have him walk away, it would tell me his exact distance from the receiver.  The accuracy can be +/- a few inches and the max range can be under 200ft. 

From what I've researched, this is possible with high-frequency RFID solutions, but the receivers are pretty expensive. You want the UHF, 800-950 MHz or so, units. The cheaper 125 kHz and 13 MHz units don't have localization capabilities for technical reasons AFAICT.
The cheapest in-stock hit I got on DigiKey for an UHF receiver was something like this: http://www.digikey.com/product-detail/en/SM-M9-MH-3.4-00D7-T0/753-1015-ND/1679645 but that seems to only do medium-field reading (3.5 meters.)

Another option is to use a small GPS module, and a small mobile phone transponder, to get the position fix to whatever the receiver is :-)

Very helpful, thanks!

tarek zidan:
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