Assessment of the FSO communication system using adaptive and MIMO MPPM with pointing errors and an atmospheric turbulence channel.

The terrestrial free space optical (FSO) communication system is attracting increased attention among the scientific and commercial research community due to its ultra-high data rate capability, licensed free large bandwidth, cost efficiency, fast and easy deployment, and secure wireless data transmission. However, the FSO system is severely affected by atmospheric conditions such as local weather conditions and fading due to turbulence. Moreover, system performance is significantly affected by pointing errors, which are caused by the misalignment between transmitter-receiver sections. Many statistical models have been proposed in the literature in order to address this significant impairment of the FSO system. In this paper, M-ary pulse position modulation (MPPM)-based FSO signal transmission over a Gamma-Gamma (G-G) fading channel is analyzed in the presence of weak to strong atmospheric turbulence and pointing errors. A multiple-input-multiple-output (MIMO) system with an equal gain combining (EGC) diversity scheme is proposed to enhance the performance of the system. The analytical closed-form expressions are obtained in terms of MeijerG-function to approximate the average bit error rate (BER) and outage probability. Furthermore, the adaptive transmission modulation (ATM) scheme is proposed to enhance the bandwidth efficiency of the FSO system link. The analytical results exhibit that the effect of turbulence and misalignment on the performance metrics (BER, outage probability) and the proposed MIMO-FSO communication link with the EGC scheme appreciably improves the system performance, and Monte Carlo simulation confirms the validation of the analytical expressions. It can also observe that bandwidth efficiency significantly improved with the proposed ATM scheme over non-adaptive counterparts.