Baseband predistorter for radio frequency power amplifiers based on a non-iterative, fast adaptation method

Adaptive digital baseband predistortion is a well known linearisation technique for removing amplitude-to-amplitude (AM/AM) and amplitude-to-phase (AM/PM) modulation that radio frequency power amplifiers (PA) produce. This paper proposes an adaptive digital baseband predistorter based on a fast adaptation, noniterative algorithm that always guarantees convergence. The PA response in a training sequence of magnitudes, after down-conversion, is used for the estimation of the predistorter´s gain table. The real and imaginary parts of the predistortion gain table are extracted in parallel without any prior polar to rectangular transformation or without extracting first the AM/AM and then the AM/PM correction table, which is the usual case. Simulation results show that, for a table size of 128, an improvement in the adjacent channel interference (ACI) of 25 dB can be achieved. The effect of the modulator/demodulator misalignment is also presented.