Contrasting MISO Schemes for IM/DD FSO Communications with Photon-Counting Receivers
In this paper, we consider the problem of Multiple-Input-Single-Output (MISO) Free-Space Optical (FSO) communications with intensity-modulation and direct-detection (IM/DD). Unlike the commonly adopted Gaussian-noise approximation, we adopt the exact Poisson statistics for the number of photons falling on the receiver. In particular, we compare three popular MISO schemes; namely, repetition coding (RC), optical spatial modulation (OSM) and spatial multiplexing (SMux). For each one of these schemes, we derive the optimal maximum likelihood (ML) decoder and we contrast the schemes in terms of rate, performance, complexity, channel state information requirements and tolerance to channel estimation errors.