A document by Naga Subrahmanya Vamsi Mohan Yarra . Click on the document to view its contents.

Free space optical system (FSO) is a wireless communication system which offers unlicensed spectrum with low cost of deployment. Losses caused by atmospheric turbulence are an enormous challenge for FSO systems. These losses are modeled by Gamma-Gamma model. The Gamma-Gamma model is used to represent moderate to strong turbulence. This model considers wind velocity, but does not consider Rainfall parameter for the calculation of refractive index structure parameter Cn2. In this research paper, we have considered effect of heavy rainfall as well as rms value of strong wind velocity which exist in hilly terrains. This modified model for the proposed spectrum-sliced wavelength division multiplexing (SS-WDM) FSO communication link incorporates differential phase shift keying (DPSK) between the popular high altitude Nilgiris Mountains from the state of Tamilnadu, India. Simulation of conventional model and the modified model by considering rainfall parameter as well as wind velocity has been demonstrated using meteorological data. The results in terms of Eye diagrams, and performance metrics such as Bit error rate (BER), log (BER), Q-factor, and Maximum eye height indicate that the modified model is more accurate for maintaining foolproof and efficient FSO communication link.

This research paper investigates free space optic (FSO) system by integrating orbital angular momentum (OAM) and polarization division multiplexing (PDM) techniques resulting in the data rate enhancement. Simulation of OAM-PDM-FSO transmission is analyzed by using Optisystem. A successful transmission of 80 Gb/s overall capacity is investigated by means of individual OAM modes (LG0,0, LG0,13, LG0,40, and LG0,80), enhancing the spectral efficiency of the system under different climatic conditions. System performance is studied for various modulation schemes including return-to-zero (RZ), non-return-to zero (NRZ) and offset-quadrature-phase shift keying (OQPSK). The best performance has been shown by means of OQPSK modulation technique. 8x10 Gb/s transmission under the influence of various external weather conditions such as rain, fog and dust is reported. A maximum FSO link range of 6 km is realized under clear weather conditions whereas a minimum FSO range of 1.25 km is achieved under heavy dust conditions. Performance of proposed hybrid OAM-PDM system is evaluated at different link lengths in terms of Q-factor, log (BER), received power and eye diagrams.