Process for properly measuring transmit power at 1 meter

[Colton Boyer]

Hello, I was wondering what the proper process is to set the measured RSSI values at 1 meter is. RSSI at 1 meter is a part of the iBeacon standard, and is also useful for non iBeacon applications. The RSSI varies greatly, however, depending on a number of factors - such as orientation of the phone, and the phone used.

A galaxy S5 I have used to test averages at about -60 (turning the phone to multiple orientations while measuring), while an S5 active averages at about -54. Another regular S5 I have used is much worse, and gets an RSSI of about -70 at 1 meter. Cases also change the RSSI by a small amount, around -4. Are there standards for measuring this? In my case, I will most likely use the S5 active's readings, as I would rather overestimate distance than underestimate.

[Hung Bui]

Hi Colton,

RSSI tells the received signal strength, it can only roughly tell about the distance. It can't be used to measure a percise distance because the received signal strength depends on many factors. It's varied from phone to phone ( becaues of the receiver on the phone), on the environment, the reflection of the signal on wall for example. As you already noticed the phone's case can also affect, same with where the user put their hand on the phone.

This is why we added a the calibrated RSSI number in the beacon setting in the nRF Beacon app. If you test with our beacon kit, and switch it to configuration mode, you can find the calibrated rssi value. This is where you can do the calibration on your specific phone, in the specific environment. So that the app can calculate the distance with a little bit more accuracy on the conversion from rssi to distance.

Depend on your application, you can have this calibration process being done automatically on the first use.