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

Marian Buschsieweke notifications at github.com
Wed Jan 13 15:46:38 CET 2021

@maribu commented on this pull request.

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

Hmm, to me it seems they are using LQI and RSSI as synonyms in the data sheet. IMO it is best to only set the RSSI value and leave the LQI value unset. For other transceivers reporting LQI in addition to RSSI provides additional information, as one cannot be converted to the other. This is here not the case. And this is also consistent with the code example linked in the [data sheet](https://infocenter.nordicsemi.com/pdf/nRF52840_PS_v1.1.pdf) on page 319: It returns only a single value and the function is named `uint8_t sample_ed(void)`. And ED is introduced as abbreviation of Energy Detection just above. So this really seems to be just the signal strength, not the link quality.

If e.g. a routing algorithm in a mesh network has to decide on costs for each link, it might base this on RSSI, LQI, and packet error rate, but ignore RSSI and LQI if those are not available. If the driver reports signal strength via both RSSI and LQI (just in different representation), the cost estimation will be biased towards stronger signals and might result in higher packet error rate.

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