Data-aided channel equalization scheme for FAST radio over fiber transmission system

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) located in Guizhou, China, is a very sensitive single dish telescope. Due to the large size of the telescope, optical fiber is used for the transmission of the 3-km astronomical signal from the telescope to the signal processing center. The optical fibers are suspended in the air above the telescope reflector, very easy to slide when the telescope feed cabin moves, resulting in phase drifts for the transmission signal. This phase drift has a negative impact on the observation mode of very long baseline interferometry, and can be compensated by the frequency transfer system in the FAST. In this manuscript, we propose a new phase drift compensation scheme, which is denoted as data-aided channel equalization scheme. The proposed scheme is based on a hypothesis of linear phase relationship between different wavelengths in the same optical fiber, and uses the channel response information of the data-aided channel to conduct signal recovery for the astronomical signal channel. Not only the phase drift, but also the frequency-dependent distortion of the broadband transmission link can be compensated. The proposed scheme has simple transmission structure, and the function part is well modularized, so that the Astronomer users can easily turn it on or off. In the proof-of-concept experiments, the estimation deviation can be significantly reduced by estimated channel responses averaging over training sequence repetitions, showing very high accuracy of the astronomical signal channel estimation.