Comparison of Different Combining Methods for Space-Diversity FSO Systems

This paper gives an overview of different signal combining schemes for free space optical (FSO) communication systems employing spatial diversity (SD) for the case of lognormal weak turbulence atmospheric channels. The receiver configurations are explained and categorized into two domains, namely optical and electrical. Moreover, a new combining scheme in the electrical domain, called "logical" domain combining, is introduced. We present closed-form expressions of bit-error-rate for the combining schemes, considering the typical case of a single-input multiple-output (SIMO) system. Through some numerical analyses, we show that depending on the number of receivers and the turbulence strength, the proposed logical combining method outperforms the other ones.