RSSI Vs Distance

[nickwch]

Hi,

I am looking into using RSSI value from RF module to estimate the distance of the transmitting source. Anyone tried this before? Signal strength is not linear to distance. I have searched the net and seems like many people would have their own way of calculating distance from the RSSI value.

Appreciate if anyone can share their experience or advise any good sites for reference.

Many Thanks.

Nicholas Wong

 

[Nigel Goodwin]

When you say 'estimate', how close an estimate are you hoping to achieve?.

Also, what is the EXACT reason for wanting to attempt it?, this could (and probably will) make a huge difference.

As for it not being linear, the reverse square law applies to RF transmissions.

 

[JimB]

I am looking into using RSSI value from RF module to estimate the distance of the transmitting source.

My first thought is that you don't have a snowflakes chance!

In a hypothetical situation, in space, yes you may get a resonable result, IF, you calibrated the system, ie with a known (and stable) transmitter power, a known (and stable) receiver sensitivity, antennae of known gain (or loss) and feeders of known loss.

In the real world on earth, the path loss between transmitter and receiver will vary due to: varying amounts of water vapour, temperature gradients in the atmosphere. There will be reflections off various objects, and off the ground itself, giving big variations in received signal strength.
An don't forget the possible equipment problems.

Do you have a particular application in mind for this technique?
Over a fixed unobstructed path, you could measure the signal strength at various points, plot them on a graph and use that to esimate where the transmitter is along the known path.
But I think you would find the results confusing and dissapointing.
And, if you deviate from the calibrated path, all bets are off!

JimB