Equivalent Baseband Models and Corresponding Digital Predistortion for Compensating Dynamic Passband Nonlinearities in Phase-Amplitude Modulation-Demodulation Schemes

摘要

We consider equivalent baseband representation of transmission circuits in the form of a nonlinear dynamical system S in discrete time (DT) defined by a series interconnection of a phase-amplitude modulator, a nonlinear dynamical system F in continuous time (CT), and an ideal demodulator. We show that when F is a CT Volterra series model, the resulting S is a series interconnection of a DT Volterra series model of the same degree and equivalent memory depth, and an LTI system with special properties. The result suggests a new, nonobvious, analytically motivated structure of digital precompensation of analog nonlinear distortions such as those caused by power amplifiers in digital communication systems. The baseband model and the corresponding digital compensation structure readily extend to OFDM modulation. MATLAB simulation is used to verify the preposed equivalent baseband model and demonstrate the effectiveness of the new compensation scheme, as compared to the standard Volterra series approach.