Closed-form suboptimal maximum-likelihood sequence detection for free-space optical communications.

In this paper, a closed-form suboptimal maximum-likelihood sequence detection (MLSD) metric and its low-complexity version are proposed for free space optical communications systems operating over lognormal fading and high signal-to-noise channel. This algorithm provides a simplification to the algorithm reported by Riediger et al. In comparison, firstly, the parameters of this algorithm are independent of the scintillation index's variation, and secondly this algorithm just contains conventional computations; it saves computational time significantly. Bit error rate performance results confirm that the proposed algorithm performs comparably well as optimal MLSD. Moreover, the low-complexity version of this algorithm consumes much less time than the previously suboptimal MLSD metric presented by Riediger et al.