multi-carrier problem in PA [hlp]

Hello Everyone;
What is the multi-carrier problem in power amplifiers? How it affects the performance of system? Can it be compensated or reduced?

Multi Carrier modulations like OFDM needs good linearity.
Sometimes all the carriers came in phase and sometimes out of phase.
So this kind of modulation has large PEAK to AVAREGE.

this is the reason the amplifier should be vary linear.
Linearizations are very popular for this kind of modulations like Pre distortion
or feed forward.