# Calculating the modulation based on the coordinates in the constellation diagram

A constellation diagram has points at the following coordinates: (2,2), (2,-2), (-2,2), (0,-2). What is the modulation used by the modem?

This is literally never explained in my textbook and I can't do it by logic, since I have NO clue what a constellation diagram is.

• Are you sure that the last coordinate isn't (-2,-2)? – Matt L. Nov 3 '14 at 17:00
• My textbook says (0,-2). I wouldn't know if it is a mistake. – user11593 Nov 3 '14 at 17:13
• If you have no clue what a constellation diagram is why don't you first check out the wikipedia article and then come back with a more concrete question? – Matt L. Nov 4 '14 at 8:57