In idle or cell_FACH mode, phenomenon of the pilot pollution is that a UE cannot firmly camp on a cell at one location because of receiving many pilot channels with similar quality (or signal strength), i.e., Ec/No (or RSCP).
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.