With the increasing requirements for larger bandwidth and higher data rate transfer of information, free space optical (FSO) communication has received growing attention in recent years. Atmospheric turbulence factors may give the most serious influence to the performance of the FSO system. In this paper, orthogonal frequency division multiplexing (OFDM) is chosen for the purpose of against channel dispersion and time varying environment. Spatial diversity is another efficient way to mitigate the effects of scintillation. We investigate the performance of OFDM FSO system of a ternary receiver with EGC reception combining scheme in log-normal distribution atmospheric turbulence channel. We analyze the probability distribution function (PDF) of the received light intensity in ternary diversity reception. Based on the simulation results, we present a comparison of the transmission performance among ternary receiver, dual receiver and single receiver system over correlated log-normal weak turbulence fading channel. The results would be useful for design and evaluation of optical wireless communication system.