Hello Famara,,
Combined BCCH means that one the TS0 of the first TRX, instead of one FULL timeslot for BCCH only, it is SHARED.
Combined BCCH (or CBC) consists of half-SDCCH and half-BCCH. In terms of capacity:
Only 3 CCCH blocks (instead of 9 blocks in a full BCCH)
Only 4 SDCCH subchannels (instead of 8 sdcch subchannels in a normal SDCCH timeslot)
Cheers,
Pix