Performance analysis of adaptive subcarrier intensity-modulated free-space optical systems - RETRACTED

Abstract

In this study, the performance of adaptive M-ary phase shift keying (MPSK)-based subcarrier intensity-modulated (SIM) free-space optical (FSO) communication system operating in K-distributed turbulence channels is investigated. The adaptive scheme is implemented by adapting the modulation order of MPSK, according to the instantaneous state of turbulence-induced fading and a pre-defined bit error rate (BER) requirement. The adaptive system requires a feedback path from the receiver to the transmitter, which is feasible for FSO channels given that scintillation is a slow time-varying process relative to the large symbol rate. First, the performance of non-adaptive system is investigated and novel, approximate closed-form expressions are derived for average BER of the system. These results will be used to benchmark the improvement in the system performance, gained by applying the adaptive modulation scheme. Then, the performance of adaptive system is considered and novel approximate, closed-form expressions for the capacity upper bound, spectral efficiency, outage probability and average BER of the adaptive SIM FSO system are presented and performance investigations under various turbulence conditions and target BER requirements are carried out. Numerical results indicate that significant spectral efficiency gains are offered without increasing the transmitted average optical power or sacrificing BER requirements.