The roadblock is the power amplifier linearity, in terms of
AM/AM and AM/PM distortions and memory effects. For non
constant envelope modulations, the PA has to be backed off,
at the detriment of the efficiency, in order to fulfill ACPR
standards requirements. For the W-CDMA, this back off is
on the order of 3-6dB, whereas for an OFDM modulation, its
value increases to 8-10dB [4]. Otherwise, either correction or
predistortion have to be employed, or alternative architectures
can be chosen.