Performance analysis of different intensity modulation techniques over atmospheric turbulent free-space optical channels.

In this paper, we introduce a comprehensive study of the performance of intensity modulation (IM) techniques over gamma-gamma (GG) distributed free-space optical (FSO) channels. We derive closed-form expressions for the average bit error rate (BER) of thermal-noise-limited FSO systems adopting various IM techniques. The effect of atmospheric turbulence is studied. Comparisons are presented in terms of the transmitted peak power to achieve a certain BER. Results show that on-off keying, pulse amplitude modulation, and expurgated pulse-position modulation (EPPM) provide superior performance compared to other IM techniques. In addition, a proposal to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) is introduced by adding another modulation layer of EPPM. A closed-form expression for the average BER of the proposed hybrid OFDM-EPPM technique over GG turbulent FSO channel is derived. Moreover, an expression for the outage probability of the FSO system adopting the proposed OFDM-EPPM technique is presented. Results are investigated and compared to those of traditional OFDM and hybrid OFDM with PPM (OFDM-PPM). It is shown that the hybrid OFDM-EPPM technique outperforms the hybrid OFDM-PPM technique for the same data rate. Moreover, the hybrid OFDM-EPPM technique allows higher data rates with lower PAPR values compared to those of the hybrid OFDM-PPM technique for the same number of time slots.