*1.1.1. What is Free Space Optics (FSO)?*

FSO is a line-of-sight technology that uses lasers to provide optical bandwidth connections or FSO is an optical communication technique that propagate the light in free space means air, outer space, vacuum, or something similar to wirelessly transmit data for telecommunication and computer networking. Currently, FSO is capable of up to 2.5 Gbps [1] of data, voice and video communications through the air, allowing optical connectivity without requiring fiberoptic cable or securing spectrum licenses. Operate between the 780 – 1600 nm wavelengths bands and use O/E and E/O converters. FSO requires light, which can be focused by using either light emitting diodes (LEDs) or lasers (light amplification by stimulated emission of radiation). The use of lasers is a simple concept similar to optical transmissions using fiberoptic cables; the only difference is the transmission media. Light travels through air faster than it does through glass, so it is fair to classify FSO as optical communications at the speed of the light. FSO communication is considered as an alternative to radio relay link line-of sight (LOS) communication systems. This chapter is concentrate on ground-to-ground free-space laser communications. FSO components are contain three stages: transmitter to send of optical radiation through the atmosphere obeys the Beer-Lamberts`s law, free space transmission channel where exist the turbulent eddies (cloud, rain, smoke, gases, temperature variations, fog and aerosol) and receiver to process the received signal. Typical links are between 300 m and 5 km, although longer distances can be deployed such as 8–11 km are possible depending

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on the speed and required availability. The importance of this chapter is to introduce the FSO technique step by step.

We will briefly focus on concept of FSO technology in section 1. Section 2 presents an optical wireless transceiver design and FSO main components and transmission media. Mathematical model of atmospheric turbulence of FSO is illustrated in section 3. Second part of this study is a case study to adapt between theoretical and practical parts of FSO technique, where series of simulations results are demonstrated and analyzed. In section 4, we demonstrate the first practical part, simulation results and discussion of geometric loss and total attenuation. The second part of case study explores the optical link budget is presented in section 5. Third part of case study shows the simulation results of BER and SNR of this proposed work is demon‐ strated in section 6. Section 7 presents some concluding remarks. Finally, we propose some important questions related to this chapter for self-evaluation.
