RSSI value vs distance

[Jefferson]

I am measuring the RSSI indoors between nRF and a cell phone.  I get these results:

Distance (ft)	RSSI (dBm)
0	-37
1	-62
2	-70
3	-75
4	-77
5	-80
6	-82
7	-82
8	-84
9	-85
10	-87

Is it expected that there is a big drop from very short range 0-1 ft and then the drop becomes very gradual at longer distances?

[Karl Ylvisaker]

Hello,

Is it expected that there is a big drop from very short range 0-1 ft and then the drop becomes very gradual at longer distances?

In short: yes, these measurements is within what is expected.
First, the dBm scale is logarithmic, so you should expect a drop similar to what you are seeing in your measurements.

Secondly, RSSI is not a very accurate measurement of distance, since there are so many factors that can degrade its performance.
A search in the forum about RSSI quality and interference yields many good discussions on this matter.

What TX power setting are you using? And, is the data samples included above averaged from multiple sample sequences?

Best regards,
Karl

[Jefferson]

Thank you.  I am using 0 dBm TX power and the data is the average value.

[Karl Ylvisaker]

Jefferson said:

I am using 0 dBm TX power and the data is the average value.

Thank you for clarifying. With this configuration I would expect similar measurements.
You could try to increase your TX power, and see if this does not "stretch" out your distances a little, but nothing is guaranteed.
A good example of a successful use-case for distancing using RSSI is the iBeacons. You could take a look at how they differentiated on the different distances ( using the notions of "near" and "far", instead of exact distances ).

Jefferson said:

Thank you.

No problem at all, I am happy to help!

Please do not hesitate to open a new ticket if you should encounter any issues or questions in the future.

Good luck with your development!

Best regards,
Karl