HAP-based Multi-hop FSO Systems Using All-Optical Relaying and Coherent Receiver

In this paper, we propose a high-altitude platform (HAP)-based multi-hop relaying free-space optic (FSO) communication system using all-optical relaying and coherent receiver. We derive a closed-form expression for the bit error rate (BER) under the effects of path loss, background noise, receiver noise, and atmospheric turbulence. Numerical results quantitatively show how the proposal outperforms a conventional HAP-based single-hop relaying system. Also, the results provide useful information for system design, such as the required transmitted power, the local oscillator power, the number of HAPs, and the optimum threshold powers at HAPs.