Modeling and Correction of Pointing Errors in Gimbals-Type Optical Communication Terminals on Motion Platforms

Abstract

In free-space optical (FSO) communication, high-precision pointing is a critical technology required for rapid acquisition to reduce link establishment time and increase communication time. FSO communication on a motion platform is necessary to expand the communication area and to promote the establishment of a global communication network. However, the pointing accuracy of an optical communication terminal on a motion platform is low due to numerous error sources and error coupling. This paper evaluates the error sources and proposes a pointing model to avoid problems resulting from error coupling. This proposed pointing model was designed to improve the pointing accuracy of a gimbals-type optical communication terminal (GOCT) on a motion platform. The effectiveness of the proposed pointing model was verified by tracking star experiments. The modified residual error of the proposed point model was 94.8 μrad compared to 1324.2 μrad without correction. Additionally, the modified residual error was 94.8 μrad of the proposed pointing model compared to 140.2 μrad of the existing model. The actual open-loop pointing error was reduced from 150.4 μrad of the existing model to 101.3 μrad of the proposed model. Thus, the pointing accuracy of a GOCT on a motion platform was significantly improved after correction by the proposed pointing model.

Pointing-Error Correction of Optical Communication Terminals on Motion Platforms Based on a K-Nearest Neighbor Algorithm

“…The nonlinear error sources are subordinate and mainly include random errors in the attitude measurements, linear approximation errors, and errors from unknown sources. Geometric errors include non-orthogonality of the azimuth and elevation axes, azimuth and elevation bearing errors, azimuth and elevation encoder errors, misalignment of the optical axis, and tube flexure [6]. The azimuth and elevation encoder errors cause inaccurate measurements of the rotation angles of the azimuth and elevation axes.…”

“…The D-H convention [1] is the most commonly used method for error source modeling. Peng et al [6] modeled the influence of each error source on pointing as a rotation matrix through the D-H convention. Applying small-angle approximations, they finally established a parameter model for linear pointing-error correction of an OCT on a motion platform.…”

“…Applying small-angle approximations, they finally established a parameter model for linear pointing-error correction of an OCT on a motion platform. In the present paper, the parameter model is reorganized as follows [6]:…”

“…The weight is distance-dependent. First, the distances between the test sample and all known samples are calculated in the attitude sensor coordinate system using Equation (6). The nearest k known samples are then selected as the nearest neighbor samples.…”

“…Fisk et al [4] addressed the geometric errors of a gimbaled pointing system using a physical mathematical model. Based on geometric error research, He et al [5] and Peng et al [6] analyzed simultaneous geometric errors and installation errors, and established a model that corrects linear pointing errors of OCTs on motion platforms.…”