Hi Rachid.
For TCH reselection beetwen segments responsible HOC parameters LAR(NON BCCH LAYER ACCESS THRESHOLD) ,LER (NON BCCH LAYER EXIT THRESHOLD), and BTS parameter NBL (NON BCCH LAYER OFFSET). Usually LAR=-85, LER=-95, NBL=5,7. Also parameter NBL must be set only for non-BCCH segment layer, because in other case you will have 99% RACH reject on cell. For GPRS reselection between segmentson Common BCCH need tune GPU & GPL parameters.
Good luck.