[riot-notifications] [RIOT-OS/RIOT] sys/inet/ieee802154/radio: fix wrong rssi conversions treewide (#15616)

Marian Buschsieweke notifications at github.com
Wed Jan 13 14:22:46 CET 2021

@maribu commented on this pull request.

One comment regarding the nRF802154 radio. But likely I'm just missing context to understand this.

> +            /* We calculate RSSI from LQI, since it's already 8-bit
+               saturated */

Maybe I'm missing context, but this comment confuses me more than it helps. I also don't quite understand how RSSI can be calculated from LQI. There doesn't seem to be a consistent definition (at least when also considering non-802.15.4 devices) for the LQI. But it seems to be mostly based on bit error rates, on "how easy a received signal can be demodulated" (citing the CC1101 datasheet), or the signal to noise ratio.

So as far as I understood, the LQI can be quite good for a weak signal (if both receiver and transmitter perform optimal and no interference, noise, scattering, reflection or other effects impacting the signal quality are present). Similar, a high RSSI doesn't necessarily mean a high LQI: E.g. when the receiver is right next to the sender, but also right next to an interfering device (e.g. an 802.11 device) the link quality can be poor.

So to my best knowledge, RSSI and LQI are orthogonal to each other and one cannot compute one from the other.

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