Idle mode mobility: cell reselection

Cell Reselection in Idle Mode

When the UE is in RRC_IDLE, it autonomously performs cell reselection based on parameters broadcast in System Information Blocks. The UE continuously measures neighboring cells and evaluates them using two criteria. The S-criteria (serving cell suitability) checks whether minimum signal requirements are met — Srxlev and Squal must both be positive for the cell to be usable. The R-criteria (cell ranking) compares the serving cell quality plus hysteresis against neighbor cell quality minus offset to determine which cell is best.