Virtual error approach to nonlinear adaptive filtering for parallel hammerstein systems

A novel virtual error approach is proposed for fully adaptive feedforward compensation/equalization, which is useful in nonlinear active noise control and predistortion for nonlinear high power amplifier (HPA). To attenuate the compensation error, two kinds of virtual error are introduced and are forced into zero by adjusting three nonlinear adaptive filters in an on-line manner. It is shown that the convergence of the compensation error to zero can be assured by forcing the virtual errors to zero separately. The proposed method can adjust the predistorter directly without identification of a post-inverse model of HPA as adopted in previous predistortion methods. The effectiveness of the proposed virtual error approach is validated in numerical simulation with comparison to an ordinary nonlinear filtered-x algorithm in the adaptive predistortion for nonlinear HPA used in OFDM communication systems.