Hi Ali,
Main cause for SD and TCH drop are : 1)Poor Coverage 2)Interference 3)HW Problem
To improve:U have to identify the cause and solve. Best way to take call traces for the particual cell and then to analyze.
SD should be assigned in the interference free TRX…and then also u can change the sd_priority..(high priority for good TRX…
Also u can set priority for tch.