Optical Wireless Communication System, Mobile Terminal Apt Study

Based on the basic theories and composition of optical wireless commu-nication system, the structure design of its APT (Acquisition, Pointing, Tracking) sub-system and further research on APT technical algorithm have been discussed theoretically in this thesis. 1550nm is chosen as the work wavelength, Cassegrain transmitting-receiving antenna as the optical antenna of the system through the elucidation of how to choose the work wavelength and optical antenna of comm-unication system. The structure and theoretical design parameter of APT sub-system have been presented through the discussion of the optical signal power estimation of APT sub-system, beam divergence angle, pointing error, and error signal extraction. Compared with existed optical wireless communication system, the design scheme proves applicable.Because of high requirement of maneuverability for the system, the beforehand emendation in APT technology has been analyzed with great exertion in the last part of the thesis. To obtain better value of beforehand emendation for maneuvering terminals, the movement characteristics of terminal must be understood well. Firstly, the motion time course for speed of 18kn under the condition of second level ocean wave was given through the numerical simulation of naval ships. Secondly, SPFM (Sliding Polynomial Fitting Method) was discussed and the arithmetic has been compared with PFM (Polynomial Fitting Method). Meanwhile, the model was corrected, and the parameters of arithmetic--system sampling frequency, the length of sliding window and the exponent of fitting polynomial--have been optimized. Finally, the small computing load and error, and the better estimation effect can be obtained when sampling frequency is more than 4Hz and sliding window is between 10 and 20 and polynomial exponent equals 3 or 4 by the computer-based simulation. When the speed of naval ships varies from 0 to 30kn, the estimated error is found increased. While the naval ships reach a certain speed, the estimated error will keep constant.