2m(But not more) as-hoc wireless range

I am looking for a way to communicate between two ardunios when they are within 2m of each other.

The limitations are:
Multiple client ardunios and a base station. (the clients are the only ones that need to know which base station)
Limited range(If they are not within about 2m then they don't communicate )
Ad-hoc (The ardunios can move in and out of each base station area.)