OAM-based multi-beam FSO transmission system for 40 Gbps data rate: performance evaluation across varying atmospheric attenuation zones in India

Abstract One way to meet the demands of high-capacity wireless links without extra bandwidth is the use of free space optical (FSO) communication techniques with orbital angular momentum (OAM) multiplexing. In this paper, a 40 Gbps OAM-based FSO transmission system using four Laguerre–Gaussian (LG) modes ( LG 0 0 ${\\mathrm{LG}}_{0}^{0}$ , LG 16 0 ${\\mathrm{LG}}_{16}^{0}$ , LG 45 0 ${\\mathrm{LG}}_{45}^{0}$ , and LG 80 0 ${\\mathrm{LG}}_{80}^{0}$ ) each transmitting 10 Gbps is explored. Analysis of the system is carried for four different Indian atmospheric conditions at Chennai, Jodhpur, Mumbai, and Srinagar. Data on atmospheric visibility for the year 2024 are retrieved from the Indian Meteorological Department and converted to attenuation coefficients with Kim model, and the annual average attenuation is taken for each city. The attenuation mean coefficient computed for Chennai is 1.13 dB/km, for Jodhpur is 4.696 dB/km, for Mumbai is 4.974 dB/km, and for Srinagar is 13.59 dB/km. Performance is determined through log(BER) and Q-factor, plotted against transmission range, and eye diagrams are analyzed at the maximum range for each city. The results indicate that attenuation and distance have a direct effect on the link performance, with Chennai, the city with the lowest attenuation, having the longest distance. The results show that the capacity of the FSO link can be greatly increased using OAM multiplexing, while the range that can be achieved is closely related to the atmospheric conditions.