Design of digital predistorters for wideband power amplifiers in communication systems with dynamic spectrum allocation

A new predistortion technique for dynamic spectrum allocation systems such as cognitive radio (CR) is proposed. The system model considered in this paper occupies a small band at a time, but the center frequency can be changed in the wide range of frequency. In this scenario, the front-end filter may not eliminate the harmonics of the power amplifier (PA) output. The proposed PD reduces the spectral regrowth of the fundamental signal at the carrier frequency (ω_ο) and removes the harmonics (2ω_ο, 3ω_ο, ⋯) at the same time. The proposed PD structure is composed of multiple predistorters (PDs) centered at integer multiples of ω_ο. The PD at ω_ο is for removing spectral regrowth of the fundamental signal, and the others are for harmonic reduction. In the proposed PD structure, parameters of PDs are found jointly. Simulation results show that the spectral regrowth can be reduced by 20dB, and the 2nd and 3rd harmonics can be reduced down to -70dB from the power of the fundamental signal.