Hi Sandeep Saraf,
yes handover failure mostly occur if there is freqency/BSIC problem (co co bsic bcch). Mobile has some time for decoding all information from neighbouring cells. Due to this fact sometimes could happen, that MS report wrong BSIC. Suddenly increase of HO failure could be due to hardware problem (one of the TRX is wrong, one of diversity is connect to the wrong antenna-direction). But also wrong parameter setting could be reason for HO failure. For example if HO access min. is to low. If you have limit for number of HO between two cells (in case of ping pong HO – HO margin between two cell is 0, or wrong settings of HCS) there is also a lot of unsuccessful HO.