The PAPR (Peak-to-Average Power Ratio) is widely
employed to measure the magnitude of the envelope fluctuations
of a given signal. It is particularly used to define the required
amplifier back-off for multi-carrier modulations such as OFDM
(Orthogonal Frequency Division Multiplexing) schemes. However,
the PAPR increases with the block size (i.e., the number of
subcarriers, in the OFDM case), but the signal’s distribution
converges to a Gaussian distribution for a large number of
subcarriers. Therefore, one might ask if the PAPR is indeed the
best parameter to define the amplifier’s back-off.
In this paper we address this issue. It is shown that the
required amplifier’s back-off for a given non-linear distortion
level, i.e. referred to the input amplifier saturation power, is
almost independent of the number of subcarriers and, therefore,
the PAPR is not the most suitable to define it. Therefore, we
recommend the use of a parameter related to the instantaneous
envelope power distribution to define the amplifier back-off.