BER Performance Of FSO Limited By Shot And Thermal Noise Over Exponentiated Weibull Fading Channels

Due to the increasing requirement for transmission speed and function of communication, and the increasing shortage of spectral bandwidth, how to improve the spectrum efficiency and improve the performance of communication has become the hotpot of research. The free space optical(FSO) communication system combines the advantage of wireless communication and optical communication. FSO can offer high speed wireless transmission with low power consumption, good security and high data rates. Nevertheless, FSO technology still has many problems which limit its development. The biggest drawback of FSO is that the transmitting signal is susceptible to the atmospheric environment, wherein the turbulence-induced intensity fluctuation, known as optical scintillation. Besides, the FSO signal would be also seriously affected by the noise. So it is of great importance to investigate the atmosphere turbulence and noise in the FSO system.To solve this problem, we analysis the influence of turbulence to signal, than, based on the Exponentiated Weibull(EW) distribution, the approximate expression for bit error rate(BER) is obtained using PPM modulation. Besides, we discuss the optimal values of APD receiver gain for different temperature, transmission distance and modulation level. The results could be a reference for the designing of FSO communication system. The main contents are as follows:1. The BER performance of FSO links adopting M-ary pulse-position modulation is investigated by considering the effects of both atmospheric turbulence and receiver noise. The atmospheric turbulence is modeled by exponentiated Weibull(EW) distribution with aperture averaging effect taken into account. For receiver noise, both shot- and thermal-noise-limited scenarios are studied and compared with log-normal(LN) and Gamma-Gamma(GG) distributions. For the shot-noise-limited system, approximate expression for BER is obtained on the basis of the generalized Gauss-Laguerre quadrature rule. The union bound of BER for the thermal-noise-limited system is also derived and verified by Monte Carlo(MC) simulation.2. The BER expression for FSO communication system over Exponentiated Weibull(EW) fading channels adopting M-ary pulse-position modulation with APD receiver is investigated. Based on the expression, the relationship between the BER performance and different temperature, transmission distance and modulation level has been investigated. It is seen that a proper selection of APD gain could significantly improve the system performance. The optimal value of APD gain remains the same for different turbulence and modulation level, nevertheless it varies significantly in according to the change of receiver noise temperature.