Enhancing FSO SISO links performance under adverse atmospheric conditions using CPPM-based DS-OCDMA: Simulation and experimental validation

Abstract

Free Space Optical (FSO) communication systems are a cost-effective solution for high-speed, secure data transmission with extensive bandwidth capabilities. However, their performance is significantly affected by atmospheric conditions, leading to challenges such as scintillation and transmission disruptions due to the inherent characteristics of photons. Recent research has focused on identifying modulation techniques that are resistant to scintillation to ensure reliable data transmission while maximizing user capacity per channel. This paper examines the use of Direct Sequence Optical Code Division Multiple Access (DS-OCDMA) in FSO links. We introduce Chaotic Pulse Position Modulation (CPPM) as a novel approach for generating DS-OCDMA sequences to enhance FSO link performance under adverse atmospheric conditions. Using Monte Carlo simulations for FSO Single Input Single Output (SISO) links, modeled with the Gamma-Gamma distribution to account for scintillation, we demonstrate that CPPM-modulated DS-OCDMA significantly outperforms conventional codes in terms of resilience to atmospheric turbulence, as evidenced by improvements in Bit Error Rate (BER). This paper also presents experimental results obtained from a fully functional, custom-built testbed designed to emulate an FSO SISO DS-OCDMA link in foggy conditions. These experimental findings not only validate the simulation results but also underscore the practical effectiveness of the proposed CPPM-modulated DS-OCDMA approach.