In BBH, your cell works like this:
each TRX-CU is transmitting only one frequency.
one call is allocated on TS3… each TDMA frame, the call changes TRX-CU. If cell has 3 TRX, then the call is allocated like this:
TDMA n1 = TRX1
TDMA n2 = TRX2
TDMA n3 = TRX3
TDMA n4 = TRX1
TDMA n5 = TRX2
TDMA n6 = TRX3
If TRX3 is faulty, you see that it impacts all the calls in the cell. Indeed, all calls in the cell are carried by all TRX. One faulty TRX is enough to degrade the whole quality.
In alcatel-lucent, the calls are not hopping from TRX to TRX. It is the TRX itself that is changing frequency. So one faulty TRX impacts only the 8 calls (or so) that it carries.