Selection diversity for wireless optical communications with non-coherent detection without CSI

The availability of Channel State Information (CSI) at the receiver side of a Free Space Optical (FSO) link is required for optimal detection and diversity combining. Consequently, providing instantaneous CSI knowledge introduces challenges to receiver design and an increase in estimation error and bandwidth waste. In this work we investigate two selection-combining diversity schemes and their achieved gains when perfect instantaneous CSI is not available. An average SNR estimation value at the receiver is used for branch selection, and signal combining is performed with branch balance and unbalance. Channel fading is modeled as a lognormal distribution with spatially correlated samples. BER performance and outage probabilities are analytically characterized. Further, analytical results are verified using computer simulation.

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