BLE beacon RSSI issues?

[PKSHER]

Hey guys I want to resolve some issues regarding RSSI values received from BLE beacons. I have ibeacons type.

1: Ibeacon format says the last byte is signal signal, is it RSSI, if so why I am having a different value in the packet and when calling NRF_LOG_RAW_INFO("RSSI2: %d\n", p_gap_evt->params.adv_report.rssi);?

2: How can we determine the approx distance wirh RSSI, and what does it mean RSSI at 1m is -77 dbm (say)?

Your suggestions will be appreciated

Thanks and Regards,

[Mttrinh]

Hi,

1. Yes, the last byte of a iBeacon packet structure are signal power. What is the difference between the two?

2. RSSI signal is too unreliable for any accurate distance measuring. The RSSI just gives you a number for the signal strength. There will always be too many variables affecting the measured RSSI, like radio interference, signal/multi-path reflections, and loss in the antenna layouts. Typically the RSSI can be used to indicate a rough estimate(for instance: far away or close).

There have been many discussions on the forum regarding this topic, you can find more here.

what does it mean RSSI at 1m is -77 dbm (say)

 Have a look at this.

[PKSHER]

Ok Thanks. So its mean for distance measurement, we need to focus on the last byte i.e. signal power rather than RSSI. And yes I have observed RSSI keeps on changing whereas signal strength is same when we donot change beacon location. 

So I am going to use signal power and this brings me to rephrase my last part. How do we determine the approx distance if say (29) is what we get as signal power.

[awneil]

Did you see my other reply?

From that description, it sounds to me that the 'signal' value is a constant for the particular beacon ?

in other words, it tells you how "loud" the beacon is.

PKSHER said:

How do we determine the approx distance

As Mttrinh already said, you really can't determine anything more than just "near" or "far".

[PKSHER]

Yes I saw the reply.

OK near or far, but how? 

[awneil]

As Mttrinh already said, the raw RSSI depends on very many things - including your particular hardware design.

So it is impossible to just give a universal formula.

You are going to have to work it out empirically.

[PKSHER]

OK now I get it. But can signal power be used to determine near or far, because its embedded in the ibeacon format as it is more stable than RSSI.

[awneil]

Think about it:

The value tells you how "loud" the beacon itself is;

How "loud" your device "hears" it will depend on both how "loud" the beacon is and how far away it is....

[PKSHER]

SO, Its mean RSSI is the one I should care abount since I am scanning beacons and determining near or far.