Initial Positioning Gps-based Laser Communications Technology Research And Implementation

Compared to a radio frequency communication system, free space optical communication provides increased security due to the transmitter-receiver line-of-sight requirement, insusceptibility to electromagnetic interference, high data rate, and unlimited bandwidth. A 5.6Gbps optical communication link has been successfully verified with a bit rate better than 10-9 between two low earth orbit satellites in Germany, May 2008. With a data rate of 5.6Gbps the laser communication links reported have been a milestone in the introduction of laser communication terminals to the space market. Therefore, researched the free space optical communication has great practical significance.Free space optical communication is a very complex task between satellites because of the small laser beam divergence which creates a complex problem for acquisition, pointing, tracking (APT), especially when there is a large distance between satellites. In free space optical communication networks, acquisition, pointing, and tracking techniques are needed to establish and maintain optical links among the static or mobile nodes in the network of satellites. It is important to align and capture the laser beams between two laser communication terminators. The primary reason for the failure of the STRV-2 satellite-to-ground lasercom experiment is the lack of acquisition.This paper presents new methods based on Global Position System (GPS) in order to accelerate the laser beam access to coarse tracking field, to speed up the establishment of optical communication link, and to resolve the uncertain area. This paper describes a precise pointing technique to steer the local directional laser beam of an optical transceiver to a target optical transceiver at a remote transceiver node. The pointing technique utilizes real-time GPS coordinates to retrieve accurate navigation information of the mobile or static platform that carries an optical transceiver. This paper focused theoretical analysis on the capture uncertain area, beam divergence, and the positioning accuracy of the initial positioning which based on GPS. Based on this related theoretical analysis, results had got that the method which this paper presented can greatly reduce the uncertain area, increase the capture probability, decrease the acquisition time, and optimize the power of laser transmitter.Designd a module based on GPS to minimize convergence time and reduce uncertain area. The incorporation of GPS sensors provides the reference information needed to establish alignment between two optical transceivers, thus eliminating the need for either of the transceivers to supply an optical beacon signal. To initiate communication between two optical transceivers, each obtains its position coordinates from the GPS sensor, which are exchanged over a general packet radio system (GPRS) link. Both sets of position coordinates are then used to calculate the azimuth and elevation angles of each of the transceivers to establish optical alignment. Through experiment using the designed module, we got the conclusion that the method can greatly reduce the uncertain area, increase the capture probability, and decrease the acquisition time, which conformed to the theoretical analysis.Resluts obtained by the theoretical analysis and experimenta of this paper provided a theoretical basis for remote optical communication. In order to accelerate beam acquisition, tracking, and speed up the link establishment of optical communication, the initial positioning of optical communications needs to be further reserch.