This paper proposes an adaptive extension of a Least Squares Volterra predistorter to compensate for the nonlinearity of the high power amplifier (HPA) with memory effects in orthogonal frequency division multiplexing (OFDM) systems at the transmitter side. Specifically, the input and output of the nonlinear HPA are accessed in the feedback loop structure to obtain the Volterra kernel parameters using least mean square (LMS) and recursive least square (RLS) algorithms. Once the Volterra kernel is obtained and signals pass through the cascaded system of the predistorter and the HPA, overall linear system characteristics are achieved. The proposed method is non-parametric as it does not assume any specific model for the HPA and the signal structure.

The performance of the proposed scheme is verified through computer simulations. The improvements in the reduction of out-of-band spectral regrowth and enhanced performance in terms of the bit error rate (BER) are documented for the travelling wave tube (TWT) HPA model.