I'm having a great deal of trouble figuring it out. I know it's far from exact, but I would like to have a reasonable estimate in meters.

Right now my device is reporting back to my the RSSI value and the tx value, but some papers that I'm looking at, such as this one are looking for values I'm not very sure of, such as the signal propagation constant or exponent.

Does anyone have any advice how I'd go about doing this?

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    \$\begingroup\$ If you install an RSSI graphing tool, you might notice that even for a constant distance, the RSSI reading will vary with time. Factors like interference from nearby devices, air pressure, humidity, channel hopping etc contribute to this uncertainty. RSSI in enclosed, electrically busy spaces is perhaps not a good measure of distance. \$\endgroup\$ – Anindo Ghosh Jan 8 '14 at 23:00
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    \$\begingroup\$ Can you tell how close someone is by how loud their voice is? \$\endgroup\$ – John U Mar 10 '14 at 13:48
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    \$\begingroup\$ What kind of accuracy are you trying to get? Indoors and with a low power device you're going to get a lot of multi-path (bad RSSI readings) and with a short range you will get a steep RSSI vs dist curve where the RSSI fluctuations will produce large estimation errors for small distances. \$\endgroup\$ – user6972 Apr 9 '14 at 8:15

Ideally the exponent will be 2 - this is what happens in free space - the power reduces proportionally to distance-squared (where the square is the exponent i.e. 2) BUT this is free space. In many urban areas and within buildings this is reckoned to increase to 3 or 4, meaning that power reduces as distance cubed or quadrupled.

Here's what I'd do - I'd calibrate my own setup - do a few tests in the environment you propose to use RSSI as distance indicator and get a feel for what the environment is like. All these papers and reports they're fine for cellular phone planners but if you want the real info on your locale do some measurements.


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