Identifying and tracking method for the beacon in intersatellite laser communications based on the fractional Fourier transform.

In satellite-to-satellite optical communications, accurate beacon tracking necessitates two optical terminals. However, during tracking, star background light noise in the receiver's charge-coupled device field of view interferes with beacon light identification, impairing system performance and communication stability, and potentially disrupting the laser communication link. The fast Fourier transform (FFT) algorithm is typically used to differentiate the beacon from starlight based on frequency characteristics. Nonetheless, when the motion trajectories of the beacon and background lights are similar and their light spots overlap, FFT has difficulty distinguishing them, causing incorrect identification of the beacon light, and then disrupting the tracking process. We introduce the fractional Fourier transform segmentation approach, which represents signals in a fractional Fourier field by rotating any angle counterclockwise around the origin in the time-frequency plane, which isolates the beacon from the background light. The method enables effective separation of the beacon light from complex scenarios, so the tracking process will not be interrupted when background light interference occurs at the terminal. This method has great value for improving the tracking performance of laser communication on the beacon light.