The EmberZNet stack (and classic EmberNet stack) provides LQI (link quality indication) for the incoming packet in the form of emberGetLastHopLqi(), as well as RSSI (receive signal strength indication) per-packet information through emberGetLastHopRssi(). Is there a direct translation between RSSI and LQI that I can apply for a given stack & radio?
There is no direct relationship between RSSI and LQI. In a quiet environment, LQI (reliability) will decrease as RSSI decreases. But if there is any interference, it is possible for LQI (reliability) to decrease with no change or an increase in RSSI. It is important to be aware that these are fundamentally different quantities, and therefore no direct equation can be applied to convert one value to the other.
Remember that LQI is measuring the reliability of a link to a particular neighboring radio, based on the BER (bit error rate) of the current packet. This is not a linear measurement, as link reliability tends to drop dramatically (almost logorithmically) as BER increases. RSSI readings simply measure peak amounts of radio energy on the channel over a given period, regardless of where that radio energy comes from.