1. Are there both SD drop and TCH drop in the same time?
2. Are TCH drops occurring in the same TRX where SDCCH is declared or SDCCH drops in one TRX and TCH drops in another? If in the same TRX then the issue is that TRX.
3. Now, what is the cause? Radio, BSS, TC drops?
4. What is interference on Idle timeslots, what is percentage of UpLink quality HO (this is to ensure you might have interference in uplink)?