hi shailendra.
first u need to find the exact reason of failure or drops.
if drop or failure are due to poor coverage, missing neighbor, interference so u need to optimize the network like( neighbor addiotion/deletion, fine tuning( priority changing),antenna optimization( changing tilt and orientation, antenna height reduction) to avoid interference( pilot pollution or u can say SC Pollution).
u need to check parameter in RNC level which can affect systemm performce.
IF capacity issue u need to increase channel element in NODE-B.