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.

[awneil]

PKSHER said:

Ibeacon format says the last byte is signal signal, is it RSSI

This page says,

"power level in 2's compliment, indicating the signal strength one meter from the device. This number must be calibrated for each device by the user or manufacturer"

[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?