the BA list contains the list of neighbor BCCH frequencies, for instance 4 neighbours = 12, 15, 21, 26
during drivetest in the serving cell, the ms listens to these 4 frequencies continously.
Now imagine the situation where the ms enters an area, where it receives a frequency ’26’, but this freq belongs to a TCH from another distant cell actually. In this situation, there is no BSIC to decode.