Designing optimized 4 × 20 Gbps FEC-NRZ scheme/HG-MDM based MMF-FSO system for last-mile 5 G users with atmospheric turbulence analysis

• High spectral efficiency is achieved with using a single wavelength for several users. • High power saving is obtained via utilizing a single power source to transmit all data users with using low cost passive optical devices. • Forward-error-correction (FEC) channel-coding with NRZ scheme and hybrid channel are supposed MMF cable and FSO transmission. • Gamma-Gamma (GG) turbulent effects (CA, WT, MT and ST) are investigated. This article presents a 4 × 20 Gbps FEC-NRZ scheme for comprising four end edge users using a single spatial laser over hybrid multimode fiber-Gamma-Gamma fibreless optical communication system with atmospheric turbulence effects based Hermite-Gaussian-mode-division-multiplexing (HG-MDM). HG modes (HG 00 , HG 01 , HG 10 and HG 11 ) are employed for four users, 20 Gbps PRBS data carries per beam resulted 80 Gbps system capacity. This study improves the survivability and reliability of various 5G faraway users in special spaces where the fiber optic may either destroy or expensive such as country side or mountains. The performance of the system is investigated in fixed MMF length of 1 Km and various FSO propagating ranges under clear-atmospheric (CA), weak-turbulence (WT), moderate-turbulence (MT) and strong-turbulence (ST) effects. The numerical outcomes visualize that 80 Gbps data transmission were successfully transmitted for FSO propagating distances of 5 Km under an ideal weather condition with log ≤ -7, while the achievable transmission distances are deteriorated to 3 Km, 1.75 Km and 1 Km with log ≤ -6, log ≤ -4 and log ≤ -5 in the presence of WT, MT and ST conditions, respectively. Our suggested design is supreme the lastly accomplished studies. Higher user data rate and transmission distance are achieved.