Adaptive Feedforward Control via Virtual Error Approach with Applications to Parallel Hammerstein Systems

A novel virtual error approach is proposed for fully adaptive feedforward control, which plays an important role 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 adaptive feedforward controller directly without identification of a forward model or post-inverse model of the nonlinear system as adopted in previous algorithms. Thus, the PE property of the reference signal is not needed, which is a great advantage of the proposed approach. Its effectiveness is examined and clarified in comparison with an ordinary nonlinear filtered-x algorithm in nonlinear active noise control and adaptive predistortion for a nonlinear HPA used in OFDM communication systems.