A Comparative Study of Modulation Schemes and Mitigation Techniques for Gamma-Gamma FSO Channels
Abstract
FSO communication systems are proven to be an effective substitute to RF technologies as FSO communication technologies boast high data rates which are not subjected to licensing and are not affected/spoiled by electromagnetic interference. However, despite these positive aspects, FSO links suffer from air turbulence which has strong detrimental effects on links and cause irradiance fluctuations (scintillation) and extreme fading. This has caused this paper to offer an in-depth performance analysis of FSO systems operating on a Gamma-Gamma turbulence channel and further explores the performance of different turbulence mitigation schemes and modulation strategies. This analysis uses OOK as a basis of comparison to other modulation schemes like 4 PPM, DPSK, and DCO-OFDM and explores the possible improvements Adaptive Optics (AO) and Dynamic Beam Steering (DBS) systems may provide to link reliability. This paper investigates the performance of DBS under three different settings: best path selection, path steering with a realistic motion model, and path steering with an alignment error. The results of many Monte Carlo simulations indicate that when it comes to turbulence, DPSK will be the best option because it adapts to changes. This paper suggests that DCO-OFDM is not optimal because it is the most adversely affected by channel fading. The best way. This works better than Adaptive Optics, especially in turbulent conditions. These results indicate that combining strong modulation techniques like DPSK with spatial diversity methods like DBS is essential for constructing dependable, high-speed free-space optical networks, even in challenging atmospheric conditions.
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