  The previous link adaptation algorithms on ofdm based systems use equal
modulation order for all sub carrier index within a block. For multimedia
transmission using ofdm as the modulation technique, unequal constellation is
used within one ofdm subcarrier block, a set of subcarriers for audio and
another set for video transmissions. A generic model has been shown for such a
transmission and link adaptation algorithm has been proposed using EESM
(Effective Exponential SNR mapping) method as basic method. Mathematical model
has been derived for the channel based on bivariate Gaussian distribution in
which the amplitude varies two dimensionally in the same envelope. From the
Moment generating function of bivariate distribution, Probability of error has
been theoretically derived. Results have been shown for BER performance of an
ofdm system using unequal constellation. BER performances have been shown for
different values of correlation parameter and fading figure.
