Simply speaking, when the number of strong cells exceeds
the active set size, there is “pilot pollution” in the area. Typically the
active set size is 3, so if there are more than 3 strong cells then there is
pilot pollution. Definition of “strong cell”: pilots within the handover window
size from the strongest cell. Typical handover window size is between 4 to 6dB.
For example, if there are more than 2 cells (besides the strongest cell) within
4dB of the strongest cell then there is pilot pollution.