Performance of SPAD-Detector in The Presence of Atmospheric Turbulence

In this paper, a novel and accurate expression for the Bit Error Rate (BER) has been developed. Additionally, the performance of a free-space optical (FSO) communication system based on a direct-detection single photon avalanche diode (SPAD) array is examined, demonstrating higher sensitivity compared to traditional photodiodes. The impact of SPAD dead time is presented. On-Off Keying (OOK) modulation is employed, given its popularity in FSO systems due to its simplicity and cost- effectiveness. Two scenarios are explored: weak turbulence conditions and the saturation region turbulence. The weak turbulence channel is modeled using the log-normal channel model, while the saturation region turbulence channel is represented by the negative exponential channel model. The accuracy of the derived expression is validated through Monte-Carlo simulation. The results from both simulation and approximation illustrate how the atmospheric channel is affected by turbulence, specifically the eddies formed due to variations in refractive index resulting from temperature fluctuations, leading to an increased Bit Error Rate (BER).