Performance analysis of index modulation based link-selection mechanism for hybrid FSO-mmWave systems

Hybrid free-space optical (FSO) and millimeter wave (mmWave) systems have emerged as promising candidates for high data rate wireless transmissions due to their unique complementary properties with respect to different channel and environment conditions. A main issue in hybrid FSO-mmWave systems is the mechanism followed to activate one of the links. Most of the proposed selection mechanisms suffer from high overhead and required side information at the transmitter. In this study, a novel selection mechanism is proposed for hybrid FSO-mmWave systems without the need for any feedback or channel state information at the transmitter side. The activation of each link, either FSO or mmWave, is determined by the use of the Index Modulation (IM) concept. The proposed IM-based link selection mechanism is analyzed in terms of spectral efficiency, average bit error rate (BER), outage probability and ergodic capacity. Moreover, it is compared to conventional switching mechanisms under various scenarios including different modulation orders, link distances, and weather conditions. In light of the numerical and simulation results, it is shown that the proposed system significantly improves the overall system performance in terms of spectral efficiency and average BER.