iBeacon calibaration

[Mohsen]

Hi everyone;

Im trying to use my nrf51822 as iBeacon with "ble_app_beacon" in SDK. As you know for estimating Distance, you should calibrate it. for calibration, place it in 1 meter and use an application like "locate" and then place it in "APP_MEASURED_RSSI" in main.c .but my questions:

• in which tx_power, I have to do calibration ? -30 , -8 , -4 or ... (Because i don't know what will i select later)

• how I have to do calibration? apple explain in "Getting Started with iBeacon". if i do this operation on a table, my data s will be correct? (or interferences that reflected from table, makes error in measuring )

thank you

[Einar Thorsrud]

You must do the calibration with the TX power you intend to use (which is up to you, depending on the range you want). The whole idea is that you calibrate for the RSSI 1 meter away from the device, and obviously the RSSI at a fixed distance will depend on the TX power.

The Calibration section in Getting Started with iBeacon describes the correct procedure. There will always be inaccuracies depending on which device you measure with, but it should be within an acceptable limit. Particularly remembering that the distance you can derive from the RSSI will in any case be inaccurate, as the signal is influenced by attenuation and multipath, particularly in a complex indoor environment.

[Mohsen]

thank you Einar. your response was clear.

another question:

I'm trying to do calibration action, with Locate. when I place my phone in 1 meter distance form my iBeacon, I press "Calibrate" botton. in this case, the app displays "CALIBRATING" blinky. after that, it says "RSSI : -60" for example. and I convert it to two's complement and enter in "#define APP_MEASURED_RSSI ". now, when I don't displace my phone and beacon, the app have to says 1 meter in Distance page. but app says 3.5 meter. I confused completely, because the app says RSSI is -60 yet and its like RSSI in calibrating time. why distance is incorrect ? (as i know, even if I place my phone 30 cm away from beacon and calibrate it, after calibrating and same distance, the app have to show 1 meter logicaly but don't. where is my mistake ?)