Closed-form BER expression for FSO links with transmit laser selection over exponential atmospheric turbulence channels

An exact closed-form expression for the average bit error rate (BER) of multiple-input-single-output free-space optical (FSO) communication systems with intensity modulation and direct detection using selection transmit diversity over strong atmospheric turbulence channels is derived. Assuming channel side information (CSI) at the transmitter and receiver, the transmit diversity technique based on the selection of the optical path with a greater value of scintillation has shown to be able to extract full diversity, outperforming other alternatives in which CSI at the transmitter is not considered.