Performance Analysis of Free Space Optical Communication Links under M-PAM and M-PSK Modulations using Adaptive Power and Modulation Techniques

Threat assessment is one of the most important pillars of data fusion systems. In this paper, we use two Free space optical (FSO) links are affected by various factors such as misalignment, dispersion, absorption and fluctuations caused by atmospheric turbulences. Meanwhile, fluctuations caused by atmospheric      turbulences occur even in a stable atmosphere. The atmospheric channels in FSO communications systems are quasi-static channels, in which the channel state information (CSI) remains constant for a long         sequence of bits. Therefore, knowing the CSI at the transmitter, transmission parameters such as power and modulation order can be adapted to reduce the effects of atmospheric turbulences. In this paper, power   and modulation order adaptation is investigated in FSO communication systems using PAM and PSK   modulations under atmospheric turbulence. To this end, three adaptive schemes referred to as adaptive power (AP), adaptive modulation (AM), and simultaneous adaptive power and modulation (APM) are    investigated. The proposed adaptive power and/or modulation schemes lead to non-convex problems in which the optimal solution is obtained by using the Lagrangian multipliers method. Finally, the  performance of the proposed schemes is evaluated and analyzed in terms of spectral efficiency and outage probability through different numerical simulations.