Have u checked the C/I on the BCCH and the non-bcch carrier’s.
Check out the foll options :
1. Where is the same BCCH freq being used in the vicinity ?
2. What are the chances that it can hit ur cell and spoil the Drop call Rate ?
3. If it is being used in the vicinity then at what height are the antenna’s mounting ?
4. Try changing the freq if ur freq plan permits u to do so or try downtilting the antenna electrically ?
For more queries email@example.com