| Optical wireless communication (FSO) technology is applied in many fields owing to its distinct characteristics, such as wide bandwidth, high secrecy capability, low cost and flexible installation. Acquisition, Pointing and Tracking (APT) technology is the key technology of design and study in the optical wireless communication system, however it is difficult to implement.In this paper the characteristics and the advantages of FSO are analyzed and the fields of its application are described firstly. Then the conceptions, the key technologies, the subsystems, the status and the tendency of FSO and APT are introduced. The acquisition,tracking and precise control technology of the APT system are deeply studied. Based on the atmospheric turbulence theory of A. N. Kolomogrov, the characters of the turbulence are analyzed, the significance of the APT in the optical wireless communication system is explained, and the typical structure of the system is discussed. The precision of the optical wireless communication system between satellites very high, but its cost is too high which prevents the popularization of the technology. In order to increase the dependability of the ground-based FSO system, a terse scheme of tracking servo is proposed.In the APT system, the digital signal process (DSP) is used as the control processor, and the related hardware platform is set up for controlling the peripheric devices. The control of the step motor, the detection of the light power, the modulation of the signal and the collection of the analog signals are realized. In the software, the basic control flow and the process of the signal are introduced, and the acquisition, pointing and tracking are realized. A new method is included in the program which allow the PC to control and renew the parameters or program in the servo system. At last, the data in the FSO system is collected continuously, the result is compared with the one without the APT system, so the feasibility of the system is proved. |
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