  This paper is concerned with digital predistortion for linearization of RF
high power amplifiers (HPAs). It has two objectives. First, we establish a
theoretical framework for a generic predistorter system, and show that if a
postdistorter exists, then it is also a predistorter, and therefore, the
predistorter and postdistorter are equivalent. This justifies the indirect
learning methods for a large class of HPAs. Secondly, we establish a systematic
and general structure for a predistorter that is capable of compensating
nonlinearity for a large variety of HPAs. This systematic structure is derived
using approximation by separable functions, and avoids selection of
predistorters based on the assumption of HPA models traditionally done in the
literature.
