Performance limitations of free-space optical communication satellite networks due to vibrations—analog case

Abstract

Free-space optical communication between satellites networked together can make possible high-speed communication between different places on earth. The use of optical radiation as a carrier between the satellites creates very narrow beam divergence angles. Due to the narrow-beam divergence angle and the large distance between the satellites, the pointing from one satellite to another is complicated. The complication is due to vibration of the pointing system caused by two stochastic fundamental mechanisms: (1) tracking noise created by the electro-optic tracker and (2) vibrations created by internal satellite mechanical mechanisms. We derive mathematical models of signal, noise, approximate SNR, and approximate bit error rates of optical communication satellite networks as functions of the system parameters, the number of satellites, and the vibration amplitude. The optical intersatellite network model considered includes transmitter satellite, repeater satellites, and receiver satellite all networked together. These models are the basis for pointing system design of appropriate complexity and performance to make the network as simple and inexpensive as possible. An example of practical communication between Anchorage in Alaska to Johannesburg in South Africa by a free-space optical communication network composed of nine low-earth-orbit satellites is given. From the analysis it is clear that even low vibration amplitude of the satellite pointing systems decreases dramatically the network performance.