## 1 Introduction  
Free space optics (FSO) is a technology that uses modulated optical beams to provide wireless data transmission [1]. Communication in this system can take place over short, medium, and also long distances. This means that use is possible for a few meters as well as up to 16 km [2]. A laser is used to create the optical beam, which means that it is necessary to have a clear line-of-sight between the devices communicating in this way. This laser is housed in a head that can operate in full duplex mode. Thus, one head is both receiving and sending. Free environment, as a term, can be understood, for example, as air or a vacuum. FSO systems work with wavelength bands from 780 to 1600 nm [3]. This means that there is no need to lease licensed frequency bands and it is also not necessary to convert the optical beam into electrical pulses as in the case of radiofrequency (RF) systems [4]. This is a huge advantage for this system. However, the biggest advantages are the large bandwidth and high data rate compared to conventional RF systems. Other advantages include ease of installation and commercial availability. Since FSO systems use an optical beam for communication, the beam angle is very narrow, which prevents intentional eavesdropping, as in this case the connection will be interrupted. Due to these advantages, these systems are used for various applications, such as aeronautical and satellite communications, temporary but also permanent connections between buildings, and so on [2].  
It is standard that communication systems must achieve a certain level of reliability. The level of this reliability must be 99.99999% for the use of communication systems. It is affected by three key factors. The first factor is the reliability of the wire and connector, by means of which data is fed to the FSO head. The second factor affecting the availability of the FSO system is the reliability of the electrical and optical components inside the head [5]. These two factors are part of fiber optics, which uses the same wires and connectors as when connecting FSO heads, and at the same time these heads use the same electrical and optical components as those used for active elements in fiber optics. The last and most important factor in the availability of the FSO system is the influence of the transmission environment, as fiber optic connections use fibers made of glass to transmit the optical beam. This means that this factor mostly affects the availability of this system and, thus, its application in the real environment [6].  
In this paper, we will focus on machine learning methods (decision trees and decision trees using the AdaBoost Regressor), which will predict the RSSI parameter for the needs of hard switching between FSO and RF lines in a hybrid FSO/RF system. The hard switching method mainly involves lower energy costs associated with the operation of the system, as in this case they do not have to transmit on both lines at the same time. Therefore, it is necessary to choose the right method of machine learning and, above all, to achieve the best possible prediction efficiency. This method was chosen based on the simplicity of implementation into the existing hybrid FSO/RF system at our laboratory and, especially, because of its advantages. The main one is the consideration of all the possible decision outcomes and the tracking of every possible path to the result, and this machine learning method comprehensively analyzes the possible consequences in each branch and identifies decision nodes where further analysis is needed.