Report RF interference levels as part of RF RESOURCE INDICATION
This means that the BSC does not have any information about the interference level within each (unused) timeslot of the given BTS.
Such interference is typically created by surrounding cells at some distance, which use the same frequency (frequency reuse) as the current cell.
OpenBSC currently doesn't use this information, but in an actual macro network deployment with high cell and frequency reuse density, the channel allocator in the BSC should prioritize assignment of new channels to thos with the least interference.
AFAIU, OsmoTRX actually does the noise measurements on UL:
but, as one can see, noise level is not being forwarded towards the BTS...