Performance limitations of free-space optical communication satellite networks due to vibrations: Direct detection digital mode

Free-space optical communication between satellites networked together can permit high data rates between different places on Earth. The use of optical radiation as a carrier between the satellites permits very narrow beam divergence. Due to the narrow divergence and the large distance between the satellites, pointing from one satellite to another is difficult. The pointing task is further complicated by vibration of the pointing system caused by tracking noise and mechanical impacts. In this work we derive mathematical performance models for digital direct detection communication satellite networks as a function of the system parameters, the number of satellites, and the vibration amplitude. The optical intersatellite network model considered includes a transmitter satellite, regenerative satellites, and a receiver satellite all networked together. A comparison between three communication system modulation schemes - on-off keying (OOK), pulse position modulation (PPM), and pulse polarization binary modulation (PPBM) - is presented. These models are the basis for optical communication tracking- and pointing-system design of appropriate complexity and performance to make the network as simple and inexpensive as possible. From the analysis it is clear that even low vibration amplitude of one satellite pointing system decreases the network performance dramatically.