ABSTRACT
This chapter analyses the effect of atmospheric turbulence on the FSO link for a range of modulation techniques. Atmospheric turbulence is known to cause signal fading in the channel where the FSO links may suffer temporary signal degradation or complete system annihilation. It is shown that OOK with a fixed threshold value is not optimum in the presence of turbulence. The PPM, SIM, and PoLSK are immune to turbulence-induced amplitude fluctuation because they require no adaptive threshold. The performance of OOK, PPM, SIM, and PoLSK schemes adopted for FSO links under atmospheric turbulence conditions (i.e., log-normal, gamma-gamma, and negative exponential channels) is further investigated in this chapter.
