Impact of radio over fiber links in feedback on linearization performances of RF power amplifiers

Radio over fiber (RoF) advanced technology is already integrated into existing 3G and 4G radio access networks where the digital unit and remote radio head equipped with the nonlinear high-power amplifiers are connected through RoF-based fronthaul links. In this study, we experimentally investigated the adaptive predistorter adjacent channel leakage (ACLR) ratio performance degradation caused by RoF links placed in both direct and feedback paths of the 3G transmitting system. We focused our investigation on the adaptive predistorter performance degradation caused by an RoF link placed in the feedback path because the distortions that originated in the feedback path define the total system distortion. With the experimental results, we show that the achieved ACLR strongly depends on RoF driving conditions. We find that there is an optimum signal level for feedback RoF that maximizes ACLR in high-power amplifier output.