Markov chain model in maximum-likelihood sequence detection for free-space optical communication through atmospheric turbulence channels

In free-space optical communication links using intensity modulation and direct detection (IM/DD), atmospheric turbulence-induced intensity fluctuations can significantly impair link performance. Communication techniques can be applied to mitigate turbulence-induced intensity fluctuations (i.e., signal fading) in the regime in which the receiver aperture 0 is smaller than the fading correlation length 0 and the observation interval 0 is smaller than the fading correlation time 0. If the receiver has knowledge of the joint temporal statistics of the fading, maximumlikelihood sequence detection (MLSD) can be employed, but at the cost of high computational complexity. In this paper, we introduce a single-step Markov chain (SMC) model for the fading correlation and use it to derive two low-complexity, suboptimal MLSD algorithms based on per-survivor processing (PSP). Simulations are presented to verify the SMC model and the performance improvement achieved using these suboptimal PSP algorithms.