A Link-Selection Mechanism for Hybrid FSO-mmWave Systems based on Index Modulation

Hybrid Free-Space Optical (FSO) and millimeter Wave (mmWave) systems have emerged as a promising candidate for high data rate wireless transmissions due to the unique complementary properties against the 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 the high overhead and the required information at the transmitter. In this study, a novel selection mechanism is proposed for hybrid FSO-mmWave systems without a 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 Index Modulation (IM) concept. The proposed link selection mechanism, called IM-based mechanism, is compared to the conventional switching mechanisms under various scenarios including different modulation orders, link distances, and weather conditions. In the light of the numerical and simulation results, it is shown that the proposed system significantly improves the overall system performance in terms of the spectral efficiency and the bit-error-rate (BER).