BEAM WIDTH AND TRANSMITTER POWER ADAPTIVE TO TRACKING SYSTEM PERFORMANCE FOR FREE-SPACE OPTICAL COMMUNICATION

The basic free-space optical communication system includes at least tw o satellites. To communicate between them, the transmitter satellite m ust track the beacon of the receiver satellite and point the informati on optical beam in its direction. Optical tracking and pointing system s for free space suffer during tracking from high-amplitude vibration because of background radiation from interstellar objects such as the Sun, Moon, Earth, and stars in the tracking field of view or the mecha nical impact from satellite internal and external sources. The vibrati ons of beam pointing increase the bit error rate and jam communication between the two satellites. One way to overcome this problem is to in crease the satellite receiver beacon power. However, this solution req uires increased power consumption and weight, both of which are disadv antageous in satellite development. Considering these facts, we derive a mathematical model of a communication system that adapts optimally the transmitter beam width and the transmitted power to the tracking s ystem performance. Based on this model, we investigate the performance of a communication system with discrete element optical phased array transmitter telescope gain. An example for a practical communication s ystem between a Low Earth Orbit Satellite and a Geostationary Earth Or bit Satellite is presented. From the results of this research it can b e seen that a four-element adaptive transmitter telescope is sufficien t to compensate for vibration amplitude doubling. The benefits of the proposed model are less required transmitter power and improved commun ication system performance. (C) 1997 Optical Society of America.