Mitigation of the Background Radiation for Free-Space Optical IM/DD Systems.

Atmospheric turbulence and pointing errors cause fluctuations in the signal intensity of the free-space optical intensity-modulation/direct-detection link. Additionally, background radiation brings a noisy photocurrent component into the received signal. Using the generalized likelihood ratio test principle, a Viterbi-type trellis-search sequence receiver is proposed, which estimates both the channel gain and the background component and detects the data sequence simultaneously. It has the advantage of a low search complexity that does not depend on the observation window length L, and its error performance approaches that of detection with perfect channel state information and no background radiation, as L becomes large.