Investigation on the performance and improvement of free space optical link in atmospheric turbulence

Abstract

Free space optical (FSO) communications, is a cost-effective and high bandwidth access technique, which is receiving growing attention with recent commercialization application. This thesis analyses the performance of FSO communication and investigates the techniques to improve the performance of free space optics. Spatial and wavelength diversity techniques are studied and the effect of diversity on the performance of FSO communication link in atmospheric turbulence conditions is analyzed. Wavelength diversity technique is used to reduce the fading under strong atmospheric turbulence condition. Mathematical expressions for the estimation of the outage probability under strong atmospheric turbulence conditions are derived and considerable improvement is found using wavelength diversity. newlinePerformance of FSO link with different wavelengths and different aperture area of optical detector has been analyzed. Effects of different wavelengths on visibility range and quality factor of optical receiver is simulated to find the performance of FSO link. It is concluded that due to reduction in scattering loss at higher wavelength; as wavelength increases, quality factor of receiver improves. Quality factor of optical receiver is also improves with increment in aperture area of detector due to increment in sensitivity of receiver due to large aperture area. newlineThe link availability calculations were made based on the power budget analysis of FSO link and on the statistical analysis of visibility data. Four different cities were selected across different geographical conditions across the country to compare the weather conditions and the performance of FSO link for different cities of India is calculated. The visibility data of the cities throughout the year is found from the website Wundermap. It is concluded that, for a given link (i.e. Transmitted power, link range, beam divergence and transmitter-receiver aperture area) the performance of FSO link is not similar for all the geographical area as the visibility conditions.