Intelligent reflecting surfaces assisted FSO and RF systems for 5G and beyond wireless communications

Abstract

With possible new use cases and hard needs of upcoming 5th generation (5G) and beyond wireless networks, the future of mobile communications appears intriguing. The propaga tion medium has been regarded as a randomly behaving entity between the transmitter and the receiver since the dawn of the modern era of wireless communications, degrading the quality of the received signal due to the uncontrollable interactions of the transmitted radio waves with the surrounding objects. On the other hand, the recent introduction of intelligent reflecting surfaces (IRS) in wireless communications allows network operators to adjust the scattering, reflection, and refraction properties of radio waves, therefore eliminating the detrimental impacts of natural wireless propagation. IRS has recently demonstrated that it can successfully regulate the wavefront of incom ing signals, including phase, amplitude, frequency, and even polarization, without the use of sophisticated decoding, encoding, and radio frequency processing methods. The IRS is a viable alternative to active reliance techniques for improving the performance of wireless systems without requiring extensive processing at the relay. In addition to this, free space optics (FSO) communication is a promising solution for high-data-rate transmission over a large bandwidth in the optical spectrum without requiring a license. The FSO operates in above 300 GHz (Infrared, Ultraviolet) range and is an emerging alternative to radio fre quency (RF) communication. Free space optics (FSO) communication is seen as a cost-effective way to provide higher bandwidth, higher data rates, better link security, higher immunity to interference, etc., com pared to radio frequency (RF) communication over short link distances. Despite these ad vantages, FSO link is severely affected by pointing errors, atmospheric turbulence, and sig nal loss due to the obstructions caused by buildings, trees, mountains, etc. In our work, we propose a hybrid and a mixed communication system model consisting of a FSO subsystem and a RF subsystem with the goal to improve the coverage and system reliability. In addition, both the FSO and RF subsystems are assisted by intelligent reflecting surfaces (IRS). Specif ically, we carry out the performance analysis of the IRS-assisted hybrid FSO/RF system and IRS-assisted mixed FSO/RF system by deriving closed-form expressions for various perfor mance metrics. The derived performance metrics have been validated using Monte-Carlo simulations. Finally, numerical results are shown along with insightful discussions.