Strange Behaviour of Adaptive SC-FDMA

Dear all, i have been simulating adaptive modulation with SCFDMA from last 2 days and each time i run the simulation i get different BERs...sometimes i get it exactly the way i wanted it to be and sometimes it got worst. Could any1 suggest me whats wrong ....i suspect there's something wrong in the channel (tapped delay line 3 taps) but i have thoroughly checked it and found no error.

Need Comments

Talha