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Free space optics (FSO) plays key role to establish a link in targeted remote and uncovered area of skip-zones where wireline (optical fiber cable) is not easy to deploy. FSO communication has been opted as a promising solution for reliable, low latency, cost effective and unlicensed spectrum wireless backhaul connectivity for 5G and beyond wireless communication system. The foremost impairments of FSO communication are atmospheric turbulence and line-of-sight (LoS) requirement between Source to Destination. To relax the LoS requirement of FSO communication, a novel scheme called intelligent reflecting surface (IRS)-assisted FSO communication is a very reliable and effective alternative solution like first-last mile access connectivity. In this work, an IRS-based FSO and radio frequency (RF) links are modeled. IRS-assisted FSO link achieves average symbol error-rate (ASER) of 10− 6 for SNR of 30 dB while FSO link with Gamma-Gamma and Malaga (M) distribution gives ASER value of 10− 3 and 10− 2 respectively. In Optical-multiple IRS-assisted FSO links, increase in number of reflecting elements improves ASER upto 10− 8 at SNR of 20dB.

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A less-complex and efficient time-hysteresis (TH)-switching algorithm assisted hybrid free-space optics (FSO)/millimeter wave (mm)-radio frequency (RF) system is presented in the paper. For improving the long-haul communication efficiency we blend a decode-and-forward (DF) relaying scheme in the proposed hybrid FSO/RF system along with maximal-ratio-combining (MRC) at receiver end for signal reconstruction.TH-switching is utilized for link transient between FSO and RF links. The exact closed-form expressions for average symbol-error-rate (ASER) and outage-probability (OP) have been derived for the performance evaluation of the system. We also present asymptotic-analysis of the ASER and OP with lower computational-complexity of the proposed system and obtain the diversity-order. To achieve target-SER value for the proposed TH-switching, the optimum-threshold-SNR value has been obtained numerically. It is observed that the proposed switching technique assisted selective-DF-relaying scheme based hybrid system along with MRC outperforms a cooperative single-FSO system as well as single-hop (SH) switching-assisted hybrid system on account of diversity as well as switching technique benefits. The proposed hybrid system achieves SER of 10− 7 in the lower SNR regimes.

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