An Integrated Scheme of Enhanced Echo State Network of Harmonic Cancellation Digital Predistortion for Short-Wave Power Amplifiers

In short-wave communication systems, the nonlinear characteristics and memory effects of high-frequency power amplifiers (HF-PAs) result in in-band intermodulation distortion (IMD) and out-of-band harmonic distortion, which significantly degrade communication quality. Digital predistortion (DPD) techniques primarily target IMD suppression; however, the harmonic components occur at integer multiples of the fundamental frequency, which is beyond the sampling bandwidth range of the DPD system. As a result, they cannot be directly modeled digitally and must be suppressed using cascaded external analog filters. To overcome these limitations, this letter proposes a novel DPD model based on an enhanced echo state network (ESN). The input signal is processed through bidirectional time delay and nonlinear order expansion, and the resulting features are fed into ESN to more effectively capture the nonlinear memory effects of HF-PA. The experimental results demonstrate that the proposed model significantly reduces IMD components and suppresses the second and third harmonics to below –59 and –62 dBc, respectively.