Weak to strong atmospheric turbulence analysis in Free Space Optical Communication and mitigation using M-ary QAM

Free Space Optical (FSO) communication involves atmosphere as a medium to setup a transmitting link between communicating nodes separated by a minimum distance. In this paper, the FSO link's performance in the presence of atmospheric turbulence and its enhancement has been suggested. We counselled the average (ergodic) capacity modelled for Gamma-Gamma optical wireless channel for various cases ranging from weak to strong atmospheric turbulence and the derivation of a closed-form mathematical expression for realizable ergodic capacity of FSO link has been done. For various values of M and different Link Ranges the Bit Error Rate (BER) of M-ARY QAM (M-Array Quadrature Amplitude Modulation) has been analysed. Further, the BER of M-ARY QAM is compared with OOK (On-Off shift Keying) and it has been found that M-ARY QAM showed better BER performance than OOK.