A Digitally Controlled Phase and Amplitude Tunable Predistortion Architecture for RoF Links

Abstract

A digitally controlled vector predistortion scheme for linearity enhancement in Radio over Fiber (RoF) link is proposed and experimentally demonstrated. The nonlinearity in the RoF link is experimentally characterized, and the designed predistorter employs a two-path structure consisting of a linear path and a nonlinear generation path, combined using a wilkinson power combiner. Digital baseband control enables precise tuning of both phase and amplitude of the predistortion signal, allowing vector alignment for effective IMD cancellation. The predistorter is placed prior to the optical transmitter to pre-compensate link nonlinearities. Across the investigated 2–60 MHz two-tone spacings, the proposed APD achieved a maximum IMD3 suppression of 20.5 dB, with a corresponding Spurious-Free Dynamic Range (SFDR) improvement of approximately 13.7 dB at 2 MHz tone spacing and Adjacent Channel Power Ratio (ACPR) reduction of 7.7 dB is obtained with a 5G-NR signal of 20-MHz bandwidth at 4-dB back-off, highlighting enhanced performance in a highly nonlinear regime. The proposed approach achieves effective linearization, validating the effectiveness of the proposed predistortion architecture for RoF links.