Joint compensation of modulator and power amplifier nonlinearities based on a complex-valued volterra model

Abstract

This paper proposes a general Volterra model for complex-valued systems and shows its application to the joint compensation of linear and nonlinear impairments of a wireless communications transmitter composed by an I/Q modulator followed by a power amplifier (PA). The proposed structure, referred to as widely nonlinear (WNL) model, sets its roots in the systematic application of complex-valued signal processing techniques. The components of the model structure are subsequently pruned through the use of a compressed-sensing algorithm that selects the active regressors from the full model. A digital predistorter (DPD) based on the WNL model was applied to the joint mitigation of a transmitter composed by a commercial vector signal generator configured with artificial impairments, followed by a preamplifier and the evaluation board of a GaN PA operating at 3.6 GHz. Measurement results showed an improved performance for the proposed linearizer compared with a DPD based on the generalized memory polynomial model, both in terms of in-band and out-of-band metrics.