TRC-Based High-Precision Spot Position Detection in Inter-Satellite Laser Communication

Abstract

Inter-satellite laser communication (Is-OWC) is one of the main space optical communication technologies currently studied in various countries. In recent years, a kind of Is-OWC communication terminal without independent beacon light has appeared. Such terminals do not have a separate beacon laser with a large divergence angle, but use a narrower communication beam to complete space capture and tracking. Therefore, the energy of the light beam divided by the acquisition, tracking, and aiming (ATP) system is greatly reduced. How to perform high-precision spot position detection under extremely low signal-to-noise ratio (SNR) is a problem that must be faced. Aiming to resolve this problem, this article proposes to use a cosine signal to modulate the intensity of the signal light, so as to convert the problem of detecting a weak light signal into the problem of detecting a line spectrum signal. The authors used the time reversal convolution (TRC) algorithm with a window function to suppress noise and enhance the spectrum line, so as to accurately detect the amplitudes of the weak photocurrents. Finally, by calculating the ratio of the photocurrent amplitude values, the precise spot position is obtained. In the experiment, when the output SNR of the four-quadrant detector (QD) is as low as −17.86 dB, the proposed method can still detect the spot position and the absolute error is limited within 0.0238 mrad.

DSM-Based Precise Pointing Angle Deviation Measurement Method for Beaconless Free Space Optical Communication

“…Compared with the direct intensity method, for which RMSE is 67.61 μrad, the proposed method can effectively improve the measurement accuracy with weak power in beaconless FSO communication. We compared the existing methods under weak power [16][17][18] with our proposed DSM-based CCR method in Table. I.…”

“…In this paper, we propose to apply the CCR algorithm [16][17][18] with four-quadrant detectors to improve the measurement accuracy of pointing angle deviation. The CCR algorithm requires the received light to be modulated a by a sine signal, which cannot be directly achieved in the beaconless case, because the light carries the communication payload.…”