Freeradius and Alvarion

Hi, I have a problem with MAC Authentication on an Alvarion Wimax base station. I use freeradius 1.1.7 with Radius Manager 3.6. Currently I am running pppoe authentication with a Mikrotik router at the backend of the Alvarion Wimax and its working fine but I need to change to MAC authentication. I have not done MAC authentication before. Thank you in advance..