Possible solutions to mitigate vibration effects in laser inter satellite links

Free space laser communication between satellites networked together can facilitate high-speed communication between different places on earth. The advantages of an optical communication system by comparison with a microwave communication system in free space are: a) smaller size and weight, b) less transmitter power, c) larger bandwidth, d) higher immunity to interference, and e) smaller transmitter beam divergence. The use of optical radiation as a carrier between the satellites engenders 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 problem is further complicated due to vibrations of the pointing system caused by two fundamental mechanisms, stochastic in nature; 1) tracking noise created by the electro-optic tracker and 2) vibrations created by internal and external mechanical mechanisms. The vibrations displace the transmitted beam and the receiver field of view with respect to one another. Such movement decreases the average received signal, and increases the bit error rate (BER). In this paper we will review five methods to mitigate the effect of vibrations on laser satellite communication system. The methods are a) receiver with adaptive detector arrays, b) Bandwidth/data rate/coding rate adaptation, c) Power minimization using adaptive beam-width, d) Communication diversity within the satellite network, and e) Power control.