White Rabbit time synchronization and data transfer for atmospheric free-space optical links

Precise time and frequency distribution is an important aspect of positioning, navigation, and timing (PNT) systems supporting commercial and military applications. Traditional radio frequency (RF) transmission of PNT information via the Global Navigation Satellite System can be compromised by a number of interference impacts including intentional methods such as jamming and spoofing as well as unintentional interference due to increased RF congestion and spectrum allocation challenges. Free-space optical communication (FSOC) technology provides an alternative to RF communication approaches in that it supports high bandwidth and data security but requires no spectral licensing. It can also serve as a mechanism to distribute PNT information in RF-challenged environments. Here, we discuss the performance characterization of a White Rabbit (WR)-based time and frequency distribution platform for FSOC links that operate in a time-varying signal channel caused by atmospheric turbulence. Time synchronization characterization of the WR timing protocol is accomplished using a scintillation playback system that imposes signal power fluctuations based on field-recorded intensity time series data under varying turbulence conditions.