CODEWITHSUNDEEP
androidbluetoothbluetooth-lowenergybeaconrssi
Helio Assad
Helio Assad

Reputation: 1

Galaxy Tab A6 reading inconsistent values for bluetooth rssi

I am using the Altbeacon library to detect and evaluate the distance from a BLE beacon in order to take some actions in my application.
I was using a Galaxy J7 device for the first tests and the result was ok. Not that precise, but precise enough.
The problem is that my target device is a Tablet Samsung Galaxy Tab A6. After I bought one, all the readings was like < 2 cm.
At first I tought it would be a calibration issue, since Tablet antenna should be much better Cell Phone.
I started the calibration process, but there was something that was not consistent: with the cell phone the RSSI readings were from -65 to -80 (between 0,25m and 20m) , which is consistent with fre space path loss, but the readings for the table were from -46 to -47 for the same distance. I tried different apps for measure, different locations, positions, everything but the result was always similar.
I tried to find someone with similar problem with no success.
I am running out of ideas of what may cause those readings, so I need some help from you guys.
1 - I think those readings are not consistent. Is that correct? Maybe I am on wrong premises
2 - What may cause those inconsistency?
3 - How can I get consistent readings?

Upvotes: 0

Views: 148

Answers (1)

davidgyoung
davidgyoung

Reputation: 64961

If you are only seeing the RSSI change by 1dB between 0.25 m and 20 m, hen that RSSI value being returned by the device is incorrect. It's unclear why, but there are at lest three possibilities:

  1. That tablet is broken. Something is wrong in the A/D converter hardware in the bluetooth chip that measures signal strength. A second device of the same model might work fine. You'd have to try another to see.

  2. That tablet model has a flawed hardware design. The way the A/D converter hardware in the bluetooth chip is hooked up has a design flaw. Every device of this model will have this same problem. Again, you'd have to try another to see.

  3. The firmware or driver does not properly convert the A/D output value from the chip to a floating point RSSI value. The chip might have an 8-bit output value from 0-255 that must be scaled in the firmware to a floating point value. Samsung may have done this improperly in the BLE driver in the Android ROM. If this is indeed the problem, you might be able to correct the RSSI in software by taking a bunch of measurements at various distances and then running an algebraic least squares regression to get a formula that will provide a good fit to an expected RSSI curve at various distances.

Upvotes: 1

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