Performance limitations of free space optical communication satellite networks due to vibrations: Heterodyne detection

Free space optical communication between satellites networked together can permit high data rates between different places on earth. In order to establish optical communication between two satellites, the line of sight of their optics must be aligned during the entire communication time. Due to the large distance between the satellites and the required accuracy, the pointing from one satellite to another is complicated. The problem is further complicated due to vibrations of the pointing system caused by two fundamental stochastic mechanisms: 1) tracking noise created by the electro-optic tracker and 2) vibrations deriving from mechanical mechanisms. Vibration of the transmitter beam in the receiver plane causes a decrease in the received optical power. Vibrations of receiver telescope relative to the received beam decrease the heterodyne mixing efficiency. These two factors increase the bit error rate (BER) of the network. In this work we derive simple mathematical models of the network BER versus the system parameters, and the transmitter and receiver vibration statistics. Considering this simple model, we propose four methods to decrease the effects of the vibration on the network performance and to converge to desired performance requirements. An example of a practical optical heterodyne free space satellite optical communication network is presented. From this research it is clear that even low amplitude vibration of the satellite pointing systems decreases dramatically network performance.