Selection diversity-aided subcarrier intensity modulation/spatial modulation for free-space optical communication

In this study, the authors investigate the performance of selection diversity-aided subcarrier intensity modulation (SIM)/spatial modulation (SM) for free-space optical communications. Selection diversity is a receiver diversity technique which can enhance reception robustness in atmospheric turbulence-induced fading. Moreover, it is most attractive in terms of the complexity when compared with the other diversity schemes. Through computer simulations, the performance of the proposed selection diversity-aided SIM/SM is compared in terms of bit error rate with that of the conventional SIM in an additive white Gaussian noise and in an outdoor environment with log-normal atmospheric channel. Furthermore, the error performance are mathematically analysed in the atmospheric turbulence channel at the spectral efficiency of 2 bits/s/Hz. Numerical results show that the performance of the proposed SIM/SM with two receivers is better than that of a conventional SIM with four receivers at the spectral efficiency of 4 bits/s/Hz. It means that the SIM/SM can release the complexity with less diversity photodetectors over the atmospheric turbulence channel. Additionally, it is shown that the performance of the proposed SIM/SM outperforms that of a conventional SIM regardless of the irradiance variance value. Therefore, the proposed selection diversity-aided SIM/SM can be a good solution to achieve reliable communication with low complexity under high spectral efficiency, even under the impaired conditions of a turbulence fading channel.