Performance Analysis of Both Shot- and Thermal-Noise Limited MultiPulse PPM Receivers in Gamma–Gamma Atmospheric Channels

The performance of free-space optical (FSO) communication systems adopting multipulse PPM (MPPM) techniques is investigated taking into account the effects of both the atmospheric turbulence and receiver noise. The atmospheric turbulence is modeled by a gamma-gamma distribution, which is suitable for both weak and strong turbulence. As for the receiver noise, both shot- and thermal-noise limited scenarios are considered. For the shot-noise limited system, both exact and approximate expressions of the average symbol-error rate (SER) of the system are obtained. For the thermal-noise limited system, a closed form for the upper bound of the average system SER, based on the Meijer G function, is obtained. Then, we validate it using Monte Carlo simulation results. Furthermore, we study the effects of changing the atmospheric conditions, operational wavelengths, and number of time slots on the average system performance. In addition, we compare the performance of the aforementioned system with that of the traditional PPM technique, in a gamma-gamma channel, under same constraints on the average energy per bit, transmission data rate, and bandwidth.