TABLE OF CONTENTS So far, the envelope amplitude distortion has only been analyzed using a two-carrier system as the excitation signal; this limits the peak-to-average RF power ratio to a single case of 3 dB. In this section, the analysis will be extended to explore the variation of distortion characteristics with more complicated envelopes, which have different peak-to-average power ratios. This is an important intermediate step to take, before considering some actual practical modulation systems such as OQPSK and DQPSK.
The easiest way in which the peak-to-average power ratio can be changed is to include one or more higher harmonics in the modulating signal,
so that by suitable choice of the number of harmonics of ? m, and the value of the m n coefficients, various kinds of envelopes can be investigated. [Note that now the m n coefficients represent the envelope of the original signal, as distinct from the ? n distortion coefficients in (9.17) and (9.18).]
One issue, which is often the subject of idle speculation, is the case of envelopes which have very high PARs due only to the random and very occasional occurrence of the high peaks. This is a common situation in dense multicarrier communications systems. The speculation concerns the appealing concept that if the high peaks are fast enough and rather infrequent, the heavy clipping which they will incur will not be noticed. This issue will be dispatched in due course, but initially a few cases will...
