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In this paper the K-Nearest Neighbor (KNN) model which is one of machine learning (ML) algorithm is applied to distinguish between the four distinct Hermite Gaussian (HG) beams (HG00, HG01, HG02, and HG03) in mode division multiplexed (MDM)-free space optics (FSO) communication system. First, the performance of the FSO system using these different HG beams is investigated for rainy weather conditions in various Indian cities having distinct geographical locations. Transmission performance is evaluated in terms of quality (Q)-factor, signal-to-noise ratio (SNR), bit error rate (BER), and eye diagrams. Then, the values of the BER for the different HG beams are applied to the KNN ML model as to classify between them. HG modes are used for capacity enhancement. Results indicate that 80 Gbps can be transmitted over 1000 m in Hyderabad, 800 m in Pune, 580 m in Chennai, and 475 m in Mumbai at log (BER) ~ 10 - 15 , Q-factor less than 8, and SNR ~ 10 dB. Additionally, the K-Nearest Neighbor (KNN) ML model shows 94% classification accuracy between four HG beams. [ABSTRACT FROM AUTHOR]

Free space optics (FSO) communication systems are preferred due to their high transmission capacity so it can support the ever-increasing volume of online traffic. Optical code division multiple access (OCDMA) is ideal for enhancing capacity by utilizing the same wavelengths for different information transmission. This paper presents a new FSO system based on the combination of orthogonal frequency division multiplexing (OFDM) and OCDMA systems. Three OCDMA channels, employing diagonal permutation shift (DPS) codes, carry 20 Gbps each, modulated by 4-level quadrature amplitude modulation (QAM) and OFDM. To assess performance, the proposed system considers severe climate conditions like rain, fog, and snow. The effectiveness is measured by bit error rate (BER) and received optical power (ROP). In addition, actual meteorological data for the cities of Alexandria, Egypt and Pune, India are evaluated to demonstrate the applicability of the proposed model in a real-world setting. The results reveal successful transmission with an overall capacity of 60 Gbps over a 3600 m FSO range in Alexandria, achieving a 0.27 dBm ROP. In Pune, with higher average rainfall, the maximum FSO link is 2750 m with a −0.06 ROP. Furthermore, the proposed model can propagate up to 850 m under weak turbulence (WT). [ABSTRACT FROM AUTHOR]