Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 15 https://internationalpubls.com Development of Opto-Electronic Free Space Optics Rain Attenuation Mathematical Model with Optisystem for Topological Optical link Analysis S. Selva Nidhyananthan1, Shilpa Prashant Kodgire2, Tilak Mukherjee3, Papun Biswas4, Jitendra Singh Tamang5, B. Ganesh Pandi6, M. Harienthiran7, Bhaskar Roy8 1,6,7Department of Electronics and Communication Engineering, Mepco Schlenk Engineering College, India. 2Department of Electronics and Telecommunication Engineering, Maharashtra Institute of Technology, India 3Department of Electronics and Telecommunication Engineering, Haldia Institute of Technology, India 4Department of Computer Science, Nahata Jogendranath Mondal Smriti Mahavidyalaya, India 5Department of Electronics and Communication Engineering, Sikkim Manipal Institute of Technology, India 5Department of Artificial Intelligence and Machine Learning, Asansol Engineering College, India nidhyan@gmail.com, spkodgire@gmail.com, mukherjeetilak@gmail.com, papunbiswas@gmail.com, js.tamang@gmail.com, ganesh.thurs@gmail.com, harienthiran2000@gmail.com, bhaskar.aiml@aecwb.edu.in Article History: Received: 10-05-2023 Revised: 05-06-2023 Accepted: 20-07-2023 Abstract: The major obstacle in free space optics FSO is how the data penetrates atmospheric attenuation disturbances like rain, fog, dust storms and snow. The performance of FSO communications is greatly influenced by how one can choose the desired modulation technique. The proposed FSO circuit is designed with a free space range stretching up to 1.85 km. Even though it covers a small radius, we can implement this technique in areas where installing fiber optic cables is impractical. The goal of the proposed work is to use this system to create a new rain attenuation model TSNGH for our region with current rainfall data. For analysis of the FSO circuit under rain attenuation conditions, different kinds of experiments and calculations are carried out with the Optisystem software. With the help of the performance measures; Q factor and BER are evaluated and improved results are accomplished. Keywords: FSO, Topological Analysis, Rain attenuation models, Modulation technique, BER, Q factor. 1. Introduction Fiber-optic communication is used to transmit data from one end to another end in the form of light pulses through the optical fiber, whereas the FSO channel is another form of optical communication technique where light is propagated through free space wirelessly to transmit data in telecommunication. Free space refers to mediums like air and a vacuum. FSO and fiber optics are both used to transmit data at a high speed rate. However, the implementation of FSO is easier to install, more scalable and more cost-effective than optical fiber communication. FSO also has a low chance of interception, resulting in higher security and smaller packing. It refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere to obtain broadband communications. FSO mainly operates between 780-1600 nm wavelength bands for electrical to optical and optical to electrical conversions. FSO is mainly used for establishing communication between spacecraft. In our demonstration, we used the Optisystem platform for simulation which helps to simulate various aspects of circuits such as how various digital and analog modulation techniques run and data transmits with different kinds of channels such as optical fiber cables, free-space optical channels, Optical wireless communications OWC and Li-Fi channels. With the help of component mailto:spkodgire@gmail.com mailto:mukherjeetilak@gmail.com mailto:papunbiswas@gmail.com mailto:js.tamang@gmail.com mailto:harienthiran2000@gmail.com Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 16 https://internationalpubls.com properties, the user can easily set the required parameters such as FSO length and varying attenuation values. The attenuation values are based on the condition of rain. Comparison of different communication systems, free space optics can be used for short-range to long-range coverage. There are a lot of applications, challenges as well as limitations in FSO [1], and many methodologies are being developed to mitigate those problems. 2. Related Works FSO performance can be impacted by various weather conditions. Simulation analyses for different weather conditions are performed at various regions in Lahore, Pakistan using an adaptive FSO/RF link and the results showed that [2], the solution to have good data rate in FSO communication links is at the penalty of increasing the transmitting power in changing weather scenarios. The adaptive system switched to RF when attenuation is high and to FSO link when attenuation is low which reduces the power requirement. The FSO performance is improved under clear and haze conditions using lesser circuitry [3] with the help of one LASER source. A simulation [4] is done using Wavelength-division multiplexing (WDM) FSO and performance is measured for clear and haze conditions while the data rate is set as 10 Gbps. Using an iterative optimization algorithm [5] and enhanced optical communication at a 10 Gbps, the performance was significantly improved for different fog, mist, rain, haze attenuation conditions. Performance analysis of FSO in rainy conditions has been investigated [6] using performance measures like Q factor, received power over a range of 1 km for existing four rain attenuation models. Magidi [7] estimated the performance of FSO with the help of the Modified Duo binary digital modulation scheme wherein the demodulator circuit came across some shortcomings. Performance of FSO is analyzed [8] using the Equal Gain Combining algorithm and differential chaos shift keying, Binary Phase Shift Keying [9] and Co-OFDM under F distribution model of channel [10]. ITU-R rain attenuation models comparison is widely studied [11-14] by researchers across the world for different topological regions. The analytic expressions for finding specific rain attenuation parameters k and Ξ± are compared with ITU-R values [15] and the relative errors are observed at any frequency in the Terahertz range [16, 18]. A performance comparison using optical detectors such as Avalanche Photo Diode APD and PIN Photo Diode was done [17]. APD gives the improved Q factor and less BER at the cost of high gain avalanched multiplication, increased biasing and response time. The challenge is obtaining good FSO performance with PIN diode having less gain. This challenge is undertaken in our models and prominent results are obtained. Our objective is on increasing Q factor and reducing BER are achieved for the existing rain attenuation models and the generated new rain attenuation model. We created our circuit using an APD detector but moved to use PIN. Our idea is to create a new predicted rain attenuation model and to analyze the performance of the FSO circuit because there is no rain attenuation model for our region. Calculations based on [11, 15-16] help to create the new rain attenuation model. 3. Proposed Work To meet increased Q and reduced BER, the FSO layout design is classified into three sections, the transmitter section, medium of transmitter, and the receiver section. The transmitter section involves a user- defined input pseudo random bit sequence generator. Continuous Wave (CW) Laser is used as a carrier to carry the input data in NRZ pulse form with the wavelength of 1550 nm (193.1 THz). The modulation technique used here is On-Off Keying OOK. Mach Zehnder (MZ) modulator is an electro-optical phase modulator that splits light into 2 halves and sends it through different paths. A high-speed electrical signal then changes the phase of the light signal in one path. 2 halves meet at the output and recombine either constructively (bright signal of 1 pulse) or destructively (no light due to signal cancellation so 0 pulse) [19]. The proposed block diagram is given in Fig.1 and the principle of the MZ modulator is represented in Fig 2. The parameter setting in FSO involves fixing a range up to 1.85 km which is almost double the distance of literature works, and attenuation Ξ± of rain calculation using the equation Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 17 https://internationalpubls.com 𝛼 = 𝐾 βˆ— 𝑅𝐻 𝑑𝑏/π‘˜π‘š (1) where, R - Rain intensity and K, H –power-law parameters Fig. 1. Block diagram of proposed FSO system In this method, attenuation due to rain conditions is considered. The modulated data from the FSO channel is passed through the photo detector like PIN or APD which is passed through a low pass Bessel filter with desired cutoff frequency of 0.75*Bit rate HZ to suppresses the noise level in the circuit. The BER analyzer is a visualizer where the performance parameters Q, and BER are analyzed. The layout design and output simulated using the optisystem given in Fig. 3 and Fig. 4. Fig. 2. MZ modulator The existing rain attenuation models with K, H values used in attenuation calculation is listed in Table 1. A model with a high Q Factor and minimum BER values is considered to be the best model. Depending on the comparisons carried out in the experiment across literature papers, Suriza model is considered the best model. We have calculated the attenuation experimentally for all the existing models using Optisystem 7.0, theoretically verified the result, also plotted the graph between Rain Intensity Vs Q Factor and Rain intensity Vs BER. Fig. 3. FSO Transmitter and Receiver layout FSO Channel Bit Sequence Generator NRZ Pulse Generator MZ Modulator Photo Detector BER Analyser CW Laser Low Pass Bessel Filter CW Input Light Beam Splitter Modulated Output Light Phase Shift Beam Combiner Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 18 https://internationalpubls.com TABLE 1. Existing Rain Attenuation Models with model parameters Model K H Carbonneau 1.076 0.67 Japan 1.58 0.63 Samir 2.03 0.74 Suriza 0.4195 0.8486 Fig. 4. FSO Output with Performance parameters We have experimented with different extinction ratios (the ratio between power in 1 pulse to 0 pulse) as given in equation 2 in MZ Modulator and observed only slight deviations as shown in Fig. 5, Fig.6, TABLE 2. The extinction ratio Re is expressed as 𝑅𝑒 = 𝑃1\𝑃0 (2) Fig. 5. Q factor for PIN with Extinction Ratio 10 dB Fig. 6. Q factor for PIN with Extinction Ratio 30 dB TABLE 2. BER for PIN With Extinction Ratio 10 dB and 30 dB Rain intensity (mm/hr) PIN With Extinction Ratio 10 dB PIN With Extinction Ratio 30 dB Carbonneau Japan Samir Suriza Carbonneau Japan Samir Suriza 1 10-10 10-7 10-5 10-17 10-15 10-11 10-8 10-26 2 10-6 10-4 10-3 10-14 10-10 10-6 10-3 10-20 3 10-5 10-3 10-2 10-10 10-7 10-4 10-2 10-16 6.2 4.58 3.8 4.78 3.4 2.5 4.03 2.3 2.4 8.44 7.48 6.06 0 2 4 6 8 10 1 2 3 Q F ac to r Rain Intensity(mm/hr) Rain Intensity Vs Q factor Carbonneau Japan Samir Suriza 7.93 6.06 4.83 6.41 4.6 3.27 5.3 2.96 2.27 10.47 9.09 7.97 0 2 4 6 8 10 12 1 2 3 Q F ac to r Rain Intensity(mm/hr) Rain Intensity Vs Q factor Carbonneau Japan Samir Suriza Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 19 https://internationalpubls.com TABLE 3. BER for APD Rain intensity (mm/hr) Carbonneau Japan Samir Suriza 1 10-103 10-56 10-36 10-91 2 10-41 10-27 10-15 10-80 3 10-31 10-17 10-9 10-62 Fig. 7. Q factor for APD Development of Rain Attenuation Model TSNGH The new model TSNGH is proposed by analyzing the operating frequency of optical communication is Gigahertz (GHz) range, but Free Space Optical Channel operates only at a frequency of terahertz (THz) which comes under the frequency band of infra-red [20, 21]. With reference to the frequency-attenuation graph [22], it is concluded that when frequency increases attenuation also increases. At higher frequencies attenuation starts to reduce and the attenuation value almost equal to the attenuation at GHz range of frequencies. Attenuation value at 193.1 THz is approximately equal to the frequency of 700 GHz. The new modal is proposed by using the formulae mentioned in the reference [16] and the values of specific attenuation are estimated and the obtained parameters like KH, HH, VK, HV are verified with the ITU Standards, and path elevation ΞΈ is deviation from the line of sight which is assumed to 5 degrees and tilt angle T is 45 degree as a rain drop is assumed to be a circular waveguide by which the K, H parameters are obtained for the proposed new model. The sample data used for developing new rain attenuation topological model TSNGH is given in Table 4. Table 4. September and October month data: Q factor and BER using PIN District September month data October month data Rainfall Intensity (mm/hr) Attenuation (dB/km) Q Factor BER Rainfall Intensity (mm/hr) Attenuation (dB/km) Q Factor BER Namakkal 1.5 1.92 5.54 10-8 1.71 2.07 5.2 10-8 Virudhunagar 1.74 2.09 5.16 10-7 1.57 1.97 5.43 10-8 Coimbatore 2.54 2.59 4.17 10-5 1.8 2.13 5.07 10-7 Thanjavur 1.25 1.73 6.01 10-10 1.58 1.98 5.41 10-8 Nilgiris 1.5 1.92 5.54 10-8 0.96 1.495 6.65 10-11 Perambalur 3.04 2.87 3.67 10-4 2.23 2.41 4.5 10-6 Tiruvannamalai 2.79 2.73 3.92 10-5 3 2.85 3.73 10-5 Ranipet 2 2.27 4.78 10-7 1.08 1.6 6.36 10-10 Madurai 1.4 1.85 5.71 10-9 1.7 2.06 5.23 10-8 Tirunelveli 1.45 1.89 5.62 10-9 1.65 2.03 5.29 10-8 Chennai 1.71 2.07 5.2 10-8 2.71 2.69 4 10-5 21.56 13.46 11.52 15.74 10.81 8.3 12.56 7.9 5.85 20.22 18.95 16.63 0 5 10 15 20 25 1 2 3 Q F ac to r Rain Intensity(mm/hr) Rain Intensity Vs Q factor Carbonneau Japan Samir Suriza Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 20 https://internationalpubls.com 4. Results and Discussion From the frequency attenuation graph, it is inferred that attenuation is the same for 700GHZ and 193.1THZ. From the recommendation ITU-R (International Telecommunication Union-Recommendation), the specific rain attenuation parameters for 700 GHz is 𝐾𝐻 = 1.4654 , 𝐻𝐻 = 0.6284 (3), 𝐾𝑉 = 1.466, 𝐻𝑣 = 0.6315 (4) 𝐾 = (𝐾𝐻 + 𝐾𝑉 + (𝐾𝐻 βˆ’ 𝐾𝑉)π‘π‘œπ‘ 2πœƒ π‘π‘œπ‘ 2𝑇) (5) 𝐻 = (𝐾𝐻𝐻𝐻 + 𝐾𝑉𝐻𝑉 + (𝐾𝐻𝐻𝐻 βˆ’ 𝐾𝑉𝐻𝑉)π‘π‘œπ‘ 2πœƒ π‘π‘œπ‘ 2𝑇 (6) πœƒ = 5 , 𝑇 = 45 π‘‘π‘’π‘”π‘Ÿπ‘’π‘’ π΄π‘‘π‘‘π‘’π‘›π‘’π‘Žπ‘‘π‘–π‘œπ‘›(𝛼) = 𝐾 βˆ— 𝑅𝐻 𝑑𝑏/π‘˜π‘š By using this formula, the K and H values are calculated as K= 1.53, H=0.566 According to Indian Meteorological department, meteorology's main monsoons are southwest monsoon and northeast monsoon. The proposed model is based on rain intensities of districts in Tamil Nadu state and the monsoon season taken for estimation mainly depends on North-East Monsoon as Tamil Nadu receives heavy rainfall during the northeast monsoon than the southwest monsoon. The heavy rainfall in Tamil Nadu is mainly during September, October and November. From Table 4, the rain intensity is estimated with the formula of attenuation (dB/km), and this attenuation is included in the FSO channel and the resultant value is analyzed using the BER analyzer which gives the parameters of Q factor, BER. The result shows that when attenuation is high, Q is low and BER is high while attenuation is low, Q factor is high, and BER is low. The BER analyzer parameters are analyzed against Rain intensity (mm/hr) Vs Q Factor and Rain Intensity Vs BER. Optimized Solution for the Developed Model TSNGH The main idea of this work is to generate a new rain attenuation model for Tamil Nadu region. Our designed model stands at position 3 compared to other existing models we considered. To further optimize the model, we focus on the following calculations. 𝐾𝐻 = {(3.8794. 10βˆ’5𝑓)(2.7474βˆ’1.7941 ln(𝑓)+1.1805𝑙𝑛2(𝑓)βˆ’0.202𝑙𝑛3(𝑓) π‘“π‘œπ‘Ÿ 1 ≀ 𝑓 ≀ 20𝐺𝐻𝑍 } {(8.2522 βˆ— 𝑓2 βˆ— 10βˆ’5/(1 βˆ’ 0.1950 𝑙𝑛(𝑓) + 6.2033 βˆ— 10βˆ’5𝑓2 π‘“π‘œπ‘Ÿ 20 ≀ 𝑓 ≀ 400𝐺𝐻𝑍} (7) 𝐻𝐻 = { (1.0564 ln(𝑓)βˆ’1.9256)2+0.9437 (1.1141 ln(𝑓)βˆ’2.0940)2+0.7181 } π‘“π‘œπ‘Ÿ 1 ≀ 𝑓 ≀ 20𝐺𝐻𝑍 {0.6828 + 0.5018 (1+2.0946βˆ—10βˆ’4𝑓(2.2862)} π‘“π‘œπ‘Ÿ 20 ≀ 𝑓 ≀ 400𝐺𝐻𝑍 (8) 𝐾𝑣 = {(3.5807 βˆ— 10βˆ’5𝑓(2.6034βˆ’1.617 ln(𝑓)+1.0940𝑙𝑛2(𝑓)βˆ’0.1877𝑙𝑛3(𝑓) π‘“π‘œπ‘Ÿ 1 ≀ 𝑓 ≀ 20𝐺𝐻𝑍 {((7.9130 βˆ— 10βˆ’5𝑓2)/(1 βˆ’ 0.1865 ln(𝑓)) + 5.9357 βˆ— 10βˆ’5𝑓2 π‘“π‘œπ‘Ÿ 20 ≀ 𝑓 ≀ 400𝐺𝐻𝑍 (9) 𝐻𝑉 = {((1.0246 ln(𝑓)) βˆ’ 1.9462)2 + (0.9048))/((1.1073(ln(𝑓)) βˆ’ 2.1584)2 + (0.6972)) π‘“π‘œπ‘Ÿ1 ≀ 𝑓 ≀ 20𝐺𝐻𝑍 {(0.6833 + ( 0.4494 1+1.8700βˆ—10βˆ’4(𝑓)(2.2862)) π‘“π‘œπ‘Ÿ 20 ≀ 𝑓 ≀ 400𝐺𝐻𝑍 (10) Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 21 https://internationalpubls.com After frequency mapping, 𝐾 = (𝐾𝐻 + 𝐾𝑉 + (𝐾𝐻 βˆ’ 𝐾𝑉)π‘π‘œπ‘ 2πœƒ π‘π‘œπ‘ 2𝑇) (11) 𝐻 = (𝐾𝐻𝐻𝐻 + 𝐾𝑉𝐻𝑉 + (𝐾𝐻𝐻𝐻 βˆ’ 𝐾𝑉𝐻𝑉)π‘π‘œπ‘ 2πœƒ π‘π‘œπ‘ 2𝑇 (12) πœƒ = 5, 𝑇 = 45 π‘‘π‘’π‘”π‘Ÿπ‘’π‘’ π΄π‘‘π‘‘π‘’π‘›π‘’π‘Žπ‘‘π‘–π‘œπ‘›(𝛼) = 𝐾 βˆ— 𝑅𝐻 𝑑𝑏/π‘˜π‘š 𝐾𝐻 = 0.7471573, 𝐾𝑉 = 0.772433874 , 𝐻𝐻 = 0.393040512, 𝐻𝑉 = 0.393346273, 𝐾 = 0.1957 𝐻 = 0.367 TABLE 5. BER comparison between the existing four models (Carbonneau, Japan, Suriza, Samir) and the new model (TSNGH) Before and After frequency mapping Rain intensity (mm/hr) Before frequency mapping After frequency mapping Carbonneau Japan Samir Suriza TSNGH Carbonneau Japan Samir Suriza TSNGH 1 10-15 10-11 10-8 10-26 10-11 10-19 10-16 10-13 10-25 10-27 2 10-10 10-6 10-3 10-20 10-7 10-15 10-11 10-8 10-21 10-26 3 10-7 10-4 10-2 10-16 10-5 10-13 10-9 10-6 10-19 10-25 From Fig. 8, Fig. 9 and Table 5, we can conclude that the new rain attenuation model TSNGH gives a better Q factor and min BER compared to other existing models. This is achieved by equalizing the frequency to 400 GHz from 700 GHz. When we have a better Q factor and min BER, we can say the system is a good performance system. After optimizing the solution our model satisfies these criteria. So, we concluded that our model achieved a good performance. Fig. 8. Comparison of Q factors for different models after frequency mapping without optimization. Fig. 9. Comparison of Q factors for different models with optimized model after frequency mapping. Conclusion In this article, we have experimentally studied attenuation of rain through the FSO channel where attenuation of different models like Carbonneau, Japan, Samir, and Suriza was analyzed with the 7.93 6.06 4.83 6.41 4.6 3.27 5.3 2.96 2.27 10.47 9.09 7.97 6.55 4.8 3.73 0 2 4 6 8 10 12 1 2 3 Q F ac to r Rain Intensity(mm/hr) Rain Intensity Vs Q factor Carbonneau Japan Samir Suriza TSNGH 8.76 7.86 7.07 8.04 6.6 5.7 7.2 5.56 4.33 10.35 9.48 8.97 10.652 10.53 10.51 0 2 4 6 8 10 12 1 2 3 Q F ac to r Rain Intensity(mm/hr) Rain Intensity Vs Q factor Carbonneau Japan Samir Suriza TSNGH Communications on Applied Nonlinear Analysis ISSN: 1074-133X Vol 30 No. 2 (2023) 22 https://internationalpubls.com performance parameters Q factor and BER. A comparison of the existing models is carried out with APD and PIN detector. A new model is created with the help of ITU-R by frequency mapping from the Frequency-attenuation graph. The real-time rain data for various districts in Tamil Nadu is collected and rain attenuation is calculated. From this, we inferred that when attenuation is high, Q factor is low and BER is high and the reverse is also true. By this inference, while the frequency range is restricted an optimized result is generated with a high Q and low BER value. By claiming the performance status of high Q and low BER the new rain attenuation model (TSNGH) is proclaimed as the Best Model among the existing model. We hope that our TSNGH model will serve as the base for future research in free-space optics to develop a new model for their topological regions. 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