Optimum table spacing in predistorting amplifier linearizers

Radio frequency (RF) power amplifiers require linearization to reduce the intermodulation (IM) power if the signal does not have a constant envelope. Digital predistortion (PD) is one of the more successful methods. However, implementations usually employ uniform spacing of the PD lookup table entries, since the question of optimum nonuniform spacing has been unresolved. This paper provides the solution: a way to compute the IM for different spacing methods, a comparison of several table spacing schemes, a derivation of the optimum table spacing method, and a demonstration that the IM of optimum spacing is only a few decibels lower than that of equal spacing by amplitude when variations in operating point are considered