Optimization of digital pulse position modulation for FSO systems: mitigating crosstalk, pointing error and ASE noise

This paper investigates the performance evaluation and enhancement of optimization techniques for digital pulse-position modulation (DPPM) and on–off keying (OOK) modulation in free-space optical (FSO) communication systems. We develop a moment generating function for the post-detection noise processes, considering a comprehensive set of key amplifier and receiver parameters, including gain and amplified spontaneous emission (ASE) noise characteristics in FSO communications. The impact of atmospheric turbulence, inter-channel crosstalk, scintillation, pointing error, and ASE noise is considered. To mitigate turbulence-induced scintillation and optical power penalties, we propose the use of aperture averaging in this study. Such a system offers power efficiency, low cost, flexibility, and reliability, making it a promising solution for future access networks and higher data rates. Numerical results demonstrate the superiority of DPPM, showing improved receiver sensitivity of approximately 9 dB at a bit-error-rate of \({10}^{-{12}}\) ${10}^{-12}$ about 9 dB for a coding level of 5 and FSO link length of 2500 m compared to an equivalent OOK non-return-to-zero approach.