Linearization of Radio-Over-Fiber Cloud-RAN Transmitters Using Pre- and Post-Distortion Techniques

This paper proposes a novel approach and apparatus along with its calibration method to use the digital predistortion (DPD) technique in radio-over fiber (RoF) cloud RAN (C-RAN) transmitters that encompass physically spaced central baseband unit (C-BBU) and remote radio head (RRH). The proposed approach requires a calibrated observation path (COP) connecting the RRH to the BBU to mitigate any hardware impairments and distortion using a broadband post-distortion technique. This feedback (FB) link provides on-demand tracking of the change in the downlink (DL) optoelectronic component's behavior and sends a copy of the radio frequency (RF) output signal to the C-BBU for DPD identification and processing. The proposed technique is experimentally validated using 40 MHz, and 100 MHz LTE-A as DL data signals, while the post-compensation model is built by a 200 MHz LTE-A signal.