Measurement Techniques for Gray-Coded WDM-FSO System with LDPC Channel-Conditioned Modulation under Atmospheric Turbulence

Measurement Techniques for Gray-Coded WDM-FSO System with LDPC Channel-Conditioned Modulation under Atmospheric Turbulence | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Measurement Techniques for Gray-Coded WDM-FSO System with LDPC Channel-Conditioned Modulation under Atmospheric Turbulence Waqar Hussain, Yousaf Khan, Farman Ali, Sultan S. Aldkeelalah, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7901223/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Free-space optical (FSO) communication has emerged as a compelling solution for high-speed data transmission due to its high bandwidth availability, security, and cost-efficient deployment. However, existing FSO systems have focused on single-channel configurations and static modulation or coding schemes, which limit the performance under dynamic atmospheric conditions. This paper presents a measurement based wavelength-division multiplexing free-space optical (WDMFSO) communication system designed to maintain reliability under atmospheric turbulence. The proposed architecture integrates Gray-coded M-ary quadrature amplitude modulation (MQAM), low-density parity-check (LDPC) coding, and a channelconditioned modulation formats driven by carrier quality indicators (CQI) and signal-to-noise ratio (SNR) thresholds. To enhance transmission across multiple wavelengths, we develop a joint physical-layer model that incorporates Gamma-Gamma turbulence, rain-induced attenuation, and geometric beam divergence based on ITU-R standards. A modulation controller adjusts the modulation order per channel according to SNR estimates, ensuring optimal spectral efficiency (SE) and bit error rate (BER) performance. Simulation results across 4 to 32 WDM channels demonstrate BER below 10−6 under atmospheric turbulence, like fog, rain and Gmma-Gamma and 10–25 mm/hr rainfall, confirming improved measuremetn accuracy and spectral efficiency compared to fixed-modulation and uncoded schemes. Measurement modeling Free space optics Wavelength division multiplexing Gray coding Low-density parity check Atmospheric turbulence mitigation Advanced modulation formats Full Text Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 11 Feb, 2026 Reviewers invited by journal 11 Feb, 2026 Editor assigned by journal 20 Oct, 2025 First submitted to journal 19 Oct, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7901223","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":589467688,"identity":"fe34eaf6-6efd-4318-9092-ca24ec416f4b","order_by":0,"name":"Waqar Hussain","email":"","orcid":"","institution":"UET: University of Engineering \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Waqar","middleName":"","lastName":"Hussain","suffix":""},{"id":589467689,"identity":"17a547ad-4e5b-4ef6-b428-8590bbcae3cd","order_by":1,"name":"Yousaf Khan","email":"","orcid":"","institution":"UET Peshawar: University of Engineering \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Yousaf","middleName":"","lastName":"Khan","suffix":""},{"id":589467690,"identity":"b19c11ee-3ccb-4b9b-b69c-25bdf7cfccc2","order_by":2,"name":"Farman Ali","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYBAC9gYYi4cHRNowMEgQ0MJzAKGFEag9jXQth4nQwn726YafOxjyDM6cPf6Yd8f5xP7ZzQcfMNTYROPUwpNudrP3DEOxwdm+xGbeM7cTZ9w5lmzAcCwttwGHFnuGNLYbvG0MiRvO8xg287bdTmy4kWMmwdhwGKcWHv5nbDf/IrScS5xPUItEGtttsC1ne0BaDiRuIKzlGdtt2TaGYskzZwxnzm1LNt54Iy3ZIAGPX3j409huvm1jyOM7k2Pw4W2bney8G8kHH3yoscGpBQr+J8BYjmCVCTjUIQO4GnsiFI+CUTAKRsEIAwA/FV897KTbfAAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-5400-9831","institution":"Qurtuba University of Sciences and Information Technology","correspondingAuthor":true,"prefix":"","firstName":"Farman","middleName":"","lastName":"Ali","suffix":""},{"id":589467691,"identity":"1abdd332-8f22-4900-975a-3a682d66d799","order_by":3,"name":"Sultan S. 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