Modulating Retroreflector-Based Satellite-to-Ground Optical Links: Joint Communications and Tracking

Abstract

Given the growing significance of CubeSats for real-time Earth monitoring and space networking, there is an increasing demand for high-speed links for CubeSats facing constraints related to the weight, dimensions, and power consumption of telecommunication equipment. This article addresses such a need by designing a modulating retroreflector (MRR)-based optical downlink system tailored for fast-moving CubeSats, highlighting joint tracking and communication operations using a single transmitter for high data rates. Key contributions encompass precise system characterization, the design of a dual-transmitter system to maximize channel capacity, derivation of channel capacity as a function of 2M + 4 random variables, and the development of an MRR-based CubeSat downlink system. Subsequently, leveraging the obtained analysis and results, we design a system with a single transmitter, enabling simultaneous tracking and communication operations through optimal adjustments of beam timing and placement in the satellite’s vicinity. Pertinent analyses demonstrate optimal laser beam adjustments to achieve maximum capacity while maintaining tracking accuracy. Monte Carlo simulations are used to validate a closed-form expression for efficient optimization of system parameters. Comprehensive simulations assess the effect of different parameters, offering crucial insights for optimal system design.