Feedback Solution for Blind Symbol Timing Recovery in Bandlimited Optical Intensity Channels

The reliable recovery of transmission parameters is of paramount importance not only for radio frequency, but also for optical wireless communication receivers. In the context of a bandlimited optical intensity link, achieved by a PAM scheme and squared raised cosine or squared double jump functions used for pulse shaping, feedforward algorithms for symbol timing estimation have been developed in recent papers published by the first author. This work is extended by the current contribution, where a feedback solution is discussed with no knowledge about data symbols. Such non-data-aided (blind) concepts are a perfect instrument to track smaller variations of the timing error affecting the payload data. It is proposed that a Gardner detector is used for the recovery loop, which is investigated with respect to open-loop characteristic, jitter performance, and acquisition behavior.