Calculating distance using RSSI values

[Usman Rashid]

Hi,

How can one calculate the distance between two beacon based on RSSI values?

How can one find location based on RSSi values of the beacons ?

What are short comings of this method ? What are the methods to cope with the short comings ?

[Jørn]

Hello Usman

Distance based on RSSI can be estimated with Friis transmission equation if you know the transmitted power and the gain of both transmitting and receiving antennas.

For a quick introduction see www.antenna-theory.com/.../friis.php

Based on the loss of received power per unit distance it could be possible to use triangulation based on RSSI values if you have several receivers.

A few of the challenges one could face, from the top of my head, is multipath propagation, multipath induced fading, obstacles preventing direct line of sight, variations in antenna gain due to directionality, and having dynamic surroundings RF-wise (moving objects, fluorescent lamps etc.).

Also beacons can be placed anywhere, meaning the environment the antenna of the beacon sees will be very varying from beacon to beacon, which will affect its characteristics.

Due to all this getting a good estimate on distance and beacon location based on RSSI can be difficult.

As for methods to cope with the shortcomings I am afraid I don't have a lot of experience in the matter.

Best regards

Jørn Frøysa