A least-squares Volterra predistorter for compensation of non-linear effects with memory in OFDM transmitters

This paper proposes a general solution to compensate for the nonlinearity of a high power amplifier (HPA) with memory effects in orthogonal frequency division multiplexing (OFDM) communication systems at the transmitter side. Mean square error (MSE) minimization is used to derive the predistorter, which is modelled as a simplified finite order Volterra system, A general feedback loop structure is used in order to reduce the computational complexity. The input and output of the nonlinear system with memory effects are accessed, and a least-squares solution is used to obtain the Volterra kernel, which represents the predistorter. Once the Volterra kernel is obtained, when signals pass through the cascaded system of the predistorter and the HPA, overall linear system characteristics are achieved. The advantage of the proposed method is that it does not assume any specific model for the HPA. The performance of the proposed scheme is verified through computer simulations. Specifically, 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.