Abstract

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.

© 2020 Optical Society of America

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