Here is what I experienced :
1.In FLP :
a. Same BSIC in 1 BTS (3 sectors) with different BCCH each sector is OK
b. Same BSIC & BCCH in nearby cells is not OK even though both cells are separated with far distance (3-4 kms), it will cause High interference
c. Same BSIC with different cells is OK as far as interference by co-channel doesn’t happen
d. Same HSN, same MAIO & MALIST in nearby cells (usually happens at the same antenna’s direction) is not OK ( if those nearby cells are separated by far distance, exg 5 km, it’s ok, but may be with low interference, you should check it by drive test) it will cause High interference (Change HSN, then it’s cleared)
a. Remember that in BCCH, each sector of a BTS or with nearby cells is designed with different frequency channel, so HSN and BSIC do not significantly affect the interference. In BBH, interference is triggered with the same frequency channel.