CODEWITHSUNDEEP
androidibeaconaltbeaconrssi
Jin
Jin

Reputation: 31

Getting RSSI value -11 is it correct?

I am working with an app that collects data( rssi value, beacon id, minor, major) from ibeacon and calculates distance. I am getting rssi value about -11 and so distance 0.0 always. is this correct rssi value? I am using altbeacon library. what is the min and max value of rssi value of ibeacon ?

Upvotes: 0

Views: 794

Answers (2)

Anders Borg
Anders Borg

Reputation: 72

To complement David's answer, an iBeacon-compatible beacon will provide a value (if configured correctly) that expresses the perceived power/RSSI when the beacon is 1 meter away. Sadly this value is often set wrong, but can provide a hint of what you should expect. It's often set to -59 dBm by default.

-11 dBm is in any case a very high power value. I just tested with a beacon set to 0 dBm and when it's very close to the phone it shows an RSSI of -36 dBm that AltBeacon translates as "immediate". 1 meter away I get "near".

I use the same library via a Cordova plugin, so I doubt AltBeacon is in the wrong in your case.

Upvotes: 0

davidgyoung
davidgyoung

Reputation: 64961

RSSI is measured in dBm, and in this case measures the strength of the signal at the receiver. The stronger the signal, the less negative the value will be. A value of -11 indicates an extremely strong signal.

Bluetooth Low Energy normally has limits on the strength of the transmission imposed by international radio regulatory agencies. A Bluetooth LE beacon transmitter that is compliant with these regulations should never put out a signal that is stronger than about -55 dBm when measured one meter away.

Moving the receiver closer to the transmitter will increase the strength of the received signal. In theory, moving from 1 meter away to 0 meters away should increase the signal by about +41 dB. This might make the maximum expected theoretical signal level at 0 meters away be read as -14 dBm. (In practice, it is impossible to get an actual distance of 0 meters -- you always have some finite distance between transmitter and receiver.)

Bottom line: A RSSI value of -11, even if measured when the receiver is touching the transmitter, is unexpectedly strong. Two possibilities:

  1. The beacon transmitter is stronger than allowed by international regulatory agencies. (Unlikely)
  2. Something is wrong with the RSSI sensor on the receiving device. There may be a problem with the Analog to Digital converter or there may be a problem with the firmware that sends the digital reading to software upstream. (Most likely)

Upvotes: 1

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