Performance investigation of wavelength diversity based BPSK-SIM FSO system under Gamma–Gamma fading and misalignment error

Free space optics (FSO) is a high-speed underwater, terrestrial and satellite communication technology. There is no necessity to get a government license for operating these communication links. FSO system is always prone to some atmospheric challenges. The light beam propagates through an open atmosphere; the refractive index fluctuation due to atmospheric turbulence impacts its properties, thus, results in a fluctuating bit error rate (BER). We obtain the closed-form expressions to investigate the average BER, outage performance of an FSO system employing binary phase-shift keying (BPSK) with subcarrier intensity modulation (SIM) and wavelength diversity. The system performance is analyzed using closed-form expressions at various atmospheric turbulence levels, attenuation, and misalignment error. The results show that the wavelength diversity based BPSK-SIM FSO system offers enhanced performance than the single input single output system.