In this paper, assuming only channel statistics information available at the receivers, we propose a transceiver design for single-input multiple-output (SIMO) free-space optical (FSO) systems over weak atmospheric turbulence, which is described by spatially correlated lognormal fading channels. To mitigate turbulence-induced spatially correlated lognormal fading, we investigate the symbol-by-symbol decision criterion and develop a low-complexity, energy-efficient transceiver by exploiting the joint spatial distribution of log irradiance. Different from existing symbol-by-symbol detection schemes, the proposed transceiver has a simple structure with asymptotical performance compared to maximum-likelihood (ML) detection and flexible modulation schemes. Computer simulations demonstrate the validity of proposed transceivers under various conditions.