Investigation of Free Space Optical Link Performance with Wavelength Diversity under Different Turbulence Conditions

Abstract

Free Space Optical (FSO) communication is rapidly growing technology in the field of wireless communication. Higher bandwidth, licence free spectrum, high security and quick deployment are the key advantages of this technology. However, the atmospheric losses due to bad weather and atmospheric turbulence are still the challenges which prevent the growth of FSO communication at a higher rate. Wavelength diversity technique has shown the capability to overcome these challenges. In this technique, the information signal is transmitted simultaneously on a different wavelength which increases the availability of FSO link and overcomes the problem of link blockage. Apart from this, each wavelength is immune against certain atmospheric elements so the use of multiple wavelengths for transmission helps to combat the atmospheric losses. Further, different wavelengths are affected differently by same atmospheric condition which makes FSO communication robust under different atmospheric turbulence conditions. newlineIn this thesis, wavelength diversity technique is applied to enhance the performance of FSO system under different turbulence conditions. Three different wavelengths of 1550, 1310 and 850 nm are chosen for this technique. Different turbulence conditions are realized by adopting well-defined channel model for a particular turbulence condition. K channel model has been considered to categorize strong turbulence condition and Exponentiated Weibull channel has been used to represent all turbulence scenarios. Outage probability and average Bit Error Rate (BER) are considered as a performance metrics. Simulations results are obtained using Matlab software. newlineThe performance of FSO system under strong turbulence with wavelength diversity technique is investigated with three different combining methods: optimal combining, equal gain combining and selection combining. Mathematical expressions are derived to evaluate average BER and outage probability. The results exhibit that wavelength diversity with optimal combining method ach