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The unmanned aerial vehicle (UAV) offers unique advantages of autonomous flight capability and small coefficient of risk, and is increasingly being used in harbor-border inspection to ensure security and orderly operation of harbors. In response to the influence of external factors such as electromagnetic interference in harbor-border inspection, this paper utilizes UAV and visible light communication (VLC) to build an efficient system to track maritime targets near the harbor reliably. In a VLC scenario, a geometrical equation for transmitter positioning is first proposed based on the received signal strength of the optical signal emitted by the target. On this basis, linear iterative positioning (LIP) using first-order Taylor expansion is proposed to realize online beam tracking. Furthermore, quadratic approximative iterative positioning (QAIP), a more precise approximation of the geometrical equation, is proposed based on second-order Taylor expansion. Simulation results show that the proposed algorithms can track targets effectively, and QAIP can achieve higher accuracy with no noise or high signal-to-noise ratio. In addition, compared with the geometrical solution, LIP and QAIP have faster computing speeds and fixed overheads.

In view of the complexity of port ship supervision and the influence of external factors such as electromagnetic interference in harbor-border inspection, an efficient system combining an unmanned aerial vehicle (UAV) and visible light positioning (VLP) is proposed for locating maritime targets. In this system, a rotatable receiver with five photodetectors (PDs) installed obliquely on UAV is designed for expanding the positioning range and allowing a lower flight altitude. On this basis, we propose the Chan–Taylor (CT) method based on time difference of arrival (TDOA) for target positioning. First, the localization problem is reformulated as a weighted least squares (WLS) problem and provides a good initial estimate via the two-step WLS (TWLS) method. Then, based on Taylor expansion of TDOA equations, estimated error is calculated using the initial estimate, which can correct the estimated position of the target iteratively. To offset the error, weighted centroid CT (WCCT) is proposed by endowing different weights based on error difference to estimated results. For further improving accuracy, a restricted-region fingerprinting positioning based on CT (CT-RFP) is proposed. In restricted area determined by CT, a certain number of fingerprints is generated based on received signal strength (RSS) for matching. Simulation results show that CT is significantly improved over the previous methods. Compared with TWLS, the accuracy of CT is improved by 49.71%. For WCCT, the maximum error is reduced from 8.65 to 6.91 cm, which effectively reduces the influence of error. Moreover, CT-RFP can achieve an accuracy within millimeter level via the appropriate number of fingerprints and ensemble runs of CT, even at high noise levels.

Visible light communication (VLC) offers a unique advantage of electromagnetic interference immunity and wide bandwidth. It has gradually become the main candidate in marine communication with great potential. As a green communication link, VLC requires reliable beam tracking as a prerequisite. Therefore, based on the received signal strength of a single-input–multiple-output system in the VLC scenario, this paper first proposes a geometrical algorithm for transmitter localization. On this basis, a linear iterative algorithm using Taylor expansion, implicit function theorem, and time-domain expansion is presented to realize online beam tracking. Under the marine VLC system, an iterative denoising algorithm based on the hidden Markov model and principal component analysis is proposed for denoising. Simulation results show that the proposed algorithms have predominance in high tracking accuracy (within 10 cm) and desirable real-time performance.