PDCH timeslots are always full-power on secondary TRX
The problem is that a dynamic TS (probably also a normal/static PDCH) is transmitting in downlink on a TRX != 0 even if there are no TBF on it (and hence no information transmitted)
The question is "how do we make sure a PDCH only transmits in DL when there is actual, real RLC/MAC blocks being transmitted".
If I remember correctly, osmo-bts-trx would not Tx anything on PDCH (idle state of TCH/F_TCH/H_PDCH) unless osmo-pcu is connected. As soon as you start osmo-pcu, it starts sending valid RLC/MAC blocks (PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK in Wireshark) to osmo-bts-trx.
In my understanding, we must ensure constant Tx power on a PDCH slot if there is at least one MS/UE is listening to it, because it needs to decode every RLC/MAC block and check the USF assignments, paging, etc. And the problem is that on the BTS side it's impossible to know if there is any TBF activity in the PCU or not, because they're basically separate entities.
understood. So it's osmo-pcu which would need to take that decision: Do we have any TBF allocations on a given timeslot? If yes -> send valid RLC/MAC blocks. If no -> send nothing (or some type of idle request) so osmo-bts doesn't transmit on those timeslots (if on TRX != 0).