Comparative Analysis of SIM-Based Hybrid Modulation Schemes Over Log-Normal Channel Model

To enhance the performance of free space optical systems, the hybrid modulation scheme has been proposed. For this analysis, the performance of different hybrid schemes has been studied in the terms of the calculated bit error rates. In this paper, SIM modulation of hybrid schemes over log-normal model has been studied. Analysis of PPM-FSK-SIM, PPM-BPSK-SIM and PPM-GMSK-SIM-based hybrid modulation schemes over the log-normal channel model has been done using MATLAB software. The performance of PPM-GMSK-SIM is proved to be better than the performance of the other two schemes in the obtained results. Although other modulation schemes may have their own advantages, PPM-GMSK-SIM scheme proposed in this paper is specifically suited to free space optical systems. The variation of BER of PPM-GMSK-SIM with the various parameters such as atmospheric turbulence and link distance has also been analyzed in this paper. In addition, the detailed comparative analysis of different schemes presented in this paper can help in choosing the appropriate modulation technique in accordance with the desired application.