CubeSat-Enabled Free-Space Optics: Joint Data Communication and Fine Beam Tracking

TL;DR

This paper presents a novel, low-complexity data detection method for CubeSat-based free-space optical links that improves beam tracking and data detection performance under size, weight, and power constraints.

Contribution

It introduces a sub-optimal blind sequence detection approach using GLRT for CubeSat FSO links, enhancing performance while reducing computational complexity.

Findings

GLRT-based detection outperforms traditional combining methods.

Proposed method achieves near-ideal receiver performance.

Beam tracking with avalanche photodiodes improves link stability.

Abstract

The integration of CubeSats with Free Space Optical (FSO) links accelerates a major advancement in high-throughput, low-Earth orbit communication systems. However, CubeSats face challenges such as size, weight, and power (SWaP) limitations, as well as vibrations that cause fluctuations in the angle-of-arrival (AoA) of the optical beam at the receiver. These practical challenges make establishing CubeSat-assisted FSO links complicated. To mitigate AoA fluctuations, we expand the receiver's field of view and track the location of the focused beam spot using an array of avalanche photodiodes at the receiver. Initially, we model the optical channel between the transmitter and the detector array. Furthermore, to reduce the computational load of maximum likelihood sequence detection, which is infeasible for CubeSats due to SWaP constraints, we propose a sub-optimal blind sequence data detection approach that relies on the generalized likelihood ratio test (GLRT) criterion. We also utilize combining methods such as equal gain combining (EGC) and maximal ratio combining (MRC) for data detection, benchmarking their performance against the GLRT-based method. Numerical results demonstrate that the proposed low-complexity GLRT-based method outperforms the combining methods, achieving performance close to that of the ideal receiver.