Free space optical communication satellite networks- Vibration effects and possible solutions

A number of serious consortiums develop satellite communication networks. The objective of these communication projects is to service personal communication users almost everywhere on earth. The inter satellite links (ISL) in those project use microwave radiation as the carrier. Free space optical communication between satellites networked together can make possible high speed communication between different places on earth. The advantages of an optical communication system instead of 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 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 problem is more complicated due to vibration of the pointing system caused by two stochastic fundamental mechanisms 1) tracking noise created by the electrooptic tracker and 2) vibrations created by internal and external mechanical mechanisms. The vibrations displace the transmitted beam in the receiver plane. Such movement of the transmitted beam in the receiver plane decreases the average received signal which decreases increases the bit error rate. In this paper we review: 1) the present status of satellite networks 2) developing efforts of optical satellite communication around the world, 3) performance results of vibration effects on different kinds of optical communication satellite networks and 4) seven approaches to overcome the problems caused by transmitter pointing vibration.