Performance Analysis of FSO DF Relays with Log-Normal Fading Channel

Abstract

Abstract This paper studies the bit error performance analysis of decode-and-forward (DF) relays-based free-space optical (FSO) communication systems using avalanche photodiode (APD). The system uses subcarrier intensity binary phase shift keying (BPSK) modulated signals and subjects to scintillation due to optical turbulence. A log-normal random process is considered to model the received signal intensity fluctuation for a clear-air condition (weak atmospheric turbulence) scenario. Mathematical expressions of the average bit error probability and bit error rate (BER) are derived by taking into account the impact of atmospheric loss, thermal-noise and shot-noise limited conditions. It can be inferred from the numerical results that using DF relay nodes can extend the transmission distance and minimize BER performance of FSO system significantly compared with the direct transmission. Moreover, the selection of APD’s gain values is essential to minimize the system’s error rate performance. Therefore, the system could achieve the minimal BER by selecting an optimal average APD gain value appropriately. Moreover, the optimal average gain values of APD significantly depend on various conditions, such as the bit rate, total transmitted power, and the number of relay nodes.