Acquisition, tracking, and pointing (ATP) mechanisms are generally adopted for optical wireless communications (OWCs) to maintain a strict alignment state for reliable communication. ATP mechanisms conventionally employ beacon lights to determine the orientation of the remote optical terminal. They typically cannot maintain a steady alignment under mobile conditions. A novel visual tracking approach is proposed to address this issue by establishing a shape beacon at the OWC terminals. The shape beacon can be sensed from virtually all directions with a camera; hence, visual tracking is an acceptable ATP solution for mobile OWCs. Results of numeric analysis indicate that visual tracking is suitable for mobile OWCs as well as conventional OWCs with acceptable accuracy. Experiments were performed to demonstrate the visual tracking procedures using the vehicle itself as the shape beacon.
An automatic alignment approach is proposed for tracking unmanned aerial vehicle (UAV) antennas by using computer vision technology. In this approach, UAV carries a low‐gain omnidirectional antenna and a ground station uses high gain directional antenna which can be driven by a pan‐tilt to point to UAV's antenna. A camera is bound together with the antenna and a computer is employed to recognize the video and control motion of the pan‐tilt, so as to move the image of UAV's antenna toward the center of the whole picture. If the distance between center of UAV image and center of the picture is kept within a few pixels, then the antennas are aligned. Performance analysis and experiment results are given, showing that the proposed antenna autoalignment approach can achieve accurate alignment of the antennas with an angle error of less than 1°.
Hybrid free‐space optical and radio frequency (FSO/RF) systems have attracted much attention for more than a decade because of their enhanced reliability and capacity as comparison to single FSO or RF systems. Existing schemes to construct such a hybrid system are usually to use either switching or encoding/decoding strategies for combination of channels. The proposed scheme, based on packet sharing strategy of Ethernet link aggregation, provides a different way to combine FSO and RF channels. Theoretical analysis and Experimental results show that the proposed scheme does enhance the reliability and utilize both channel capacities for a multi‐channel system. Moreover, this scheme is simple and scalable because more channels can be combined based on such a packet sharing strategy without modifying the physical channel structures, therefore, this scheme may provide a good solution for constructing an efficient and cost‐effective hybrid FSO/RF system.
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