This seems like a very broad question. There are varied reasons why an intra-cell Ho is required.
1. Moving from FR to HR or HR to FR channel. Congestion based thresholds control these like new_calls_hr, etc.
2. Moving from GSM to DCS and DCS to GSM for concentric cells here leavel based thresholds define when HO Takes place. like Zone_Ho_Hyst, rxlev_ul/dl_zone and inner_zone_alf.
3. Frequency change HO ( BCCH to Hopping / GSM to DSC) to preserve quality, here quality and leavel thresholds control the HO.