Multiple input multiple output (MIMO) technique with equal gain combining (EGC) is considered in this work to enhance the data rate of free-space optical communication (FSO) system in log-normal channel. In FSO system, light propagating in free space is used to transmit data for communication system. 256-ary pulse position modulation (PPM) using intensity modulation with direct detection (IM/DD) as a power efficient system is employed using PIN receiver. Obtained results demonstrate that

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... cant boost of data rate can be achieved using MIMO techniques. Data rate enhances from 350 Mbps to 800 Mbps when using 2 × 2 MIMO configuration. As well, 1 Gbps is reported for 4 × 4 MIMO system. These enhancements are achieved without any bandwidth or power expansions and the bit error rate (BER) at the receiver is maintained below 10 −3 . Index Terms-Free-space optical communications (FSO), Mary pulse position modulation (M -ary PPM), Multiple input multiple output (MIMO), Log-normal channel, PIN receiver.