Quantum Limits of LEO Satellite Beacon Reading

TL;DR

This work analyzes the quantum limits of reading weak optical beacons from LEO satellites, framing beacon identification as a multi-hypothesis problem and comparing conventional Shannon-limited receivers with quantum receivers that can operate at the Holevo limit. By modeling the link as a lossy bosonic channel and using joint detection, the study shows that a Joint Detector Receiver (JDR) can achieve a substantial capacity advantage, translating into a dramatically reduced Time-To-Read (TTR) and a much larger Active Time Window (ATW) under adverse weather. Finite-block-length corrections are found negligible for the proposed code lengths (~10^6 channel uses), allowing focus on asymptotic capacities $C_S$ and $C_H$. The results highlight practical design needs—extremely narrow spectral filters, short-term quantum memories, and non-destructive photon counting—and discuss network implications for large satellite constellations, suggesting a shift of complexity toward ground receivers to enable scalable beacon reading in future quantum-enabled space networks.

Abstract

We study the quantum limits of the ELROI beacon concept introduced by Holmes, Weaver, and Palmer. In this concept, a satellite continuously emits a weak optical signal to broadcast its identity. Via analysis of the fundamental limits on communication introduced by Shannon, Gordon, and Holevo, we demonstrate that in such scenarios, incorporating quantum technology into the design of a ground station significantly enhances performance. Specifically, the Time-To-Read the beacon signal and thereby identify the satellite is greatly reduced in situations where weather conditions obstruct the signal, allowing the Active Time Window, during which the satellite can be utilized for subsequent network operations, to be extended by nearly a factor of 20. In this particular case, the quantum technology concept that is employed is the so-called Joint Detector Receiver, which is a system aiming to operate at the Gordon-Holevo limit by performing joint quantum operations on sequences of incoming signals.

Figures (3)

• Figure 1: satellite and base station. Depicted is the elevation angle $\theta$.
• Figure 2: Shown is the time in seconds that the ground station requires to read the beacon ID, referred to as the , plotted against the satellite's elevation angle above the horizon at the moment the reading begins when the satellite's orbital height is $1,000$ km.
• Figure 3: The figure shows the of the satellite as a function of the elevation angle at which the ground station begins to read the beacon ID when the satellite's orbital height is $1,000$ km.