The condition to determine the area has pilot pollution in idle or cell_FACH mode is that third pilot appears in the cell re-selection region.
In cell_DCH mode, phenomenon of the pilot pollution is that a UE at one location frequently changes its active set cells (active set update rate is very high) because of receiving many pilot channels with similar quality (or signal strength), i.e., Ec/No (or RSCP). It causes high signaling load in RRC and Iub interfaces and the capacity of RNC is consequently reduced.
The condition to determine the area has pilot pollution in cell_DCH mode is the number of pilots within the Reporting Range 1b: threshold for drop window range is larger than Max Active Set.
Possible solutions to overcome pilot pollution shall be:
The direct solution is to remove the cells overlapping by changing the antenna configurations or reducing pilot powers of the unwanted cells.
The most effective solution is to increase the pilot channel power Primary CPICH power of the desired cell.
For the pilot pollution in idle or cell_FACH mode, Q Offset 2sn (CPIC RSCP) parameter of the desired cell can be increased to create a dominated cell.
