How to retrieve main entity values within a filter expression of a parameter

Hi,

How can I access to main entity fields from filter expression of a combo parameter which is defined in a collection that is defined in the main entity?

Example: I have a Main Entity named "ME" which has a field "ME_F". "ME" has a Collection named "COL". The "COL" has a relation to a parameter named "PA" which has two fields, "PA_Name" and "PA_F". I want to write a filter expression in "PA" combo field in "COL" two show the "PA" values which their "PA_F" value is equal to "ME_F" value. Now, I don't know how to access "ME_F" in the "PA" filter expression.