Publications Conference paper · Mega-constellations · 2025

Modeling Pointing, Acquisition, and Tracking Delays in Free-Space Optical Satellite Networks

Jason Gerard, Juan A. Fraire, and Sandra Céspedes

IEEE International Conference on Wireless for Space and Extreme Environments (WiSEE), pp. 1–6, 2025

Abstract

Free-space optical communications enable high-capacity optical inter-satellite links (OISL) and direct-to-Earth (DTE) links, but require precise Pointing, Acquisition, and Tracking (PAT) between terminals. Current scheduling approaches often overlook or oversimplify PAT delays, leading to inefficient contact planning and overestimated network capacities. We present a validated model for quantifying PAT delays before data transmission begins, encompassing coarse pointing, fine pointing, and the handover to tracking. The model is grounded in mission data from NASA TBIRD, LLCD, DSOC, and ESA’s Lunar Optical Communication Terminal. We find that PAT delays exhibit multimodal distributions based on prior link geometry and scale nonlinearly with initial pointing uncertainty and optical beam width. Integrating these delay models into routing and scheduling algorithms will enable more accurate contact planning and higher utilization in optical networks. The proposed model provides a foundation for evaluating performance and designing algorithms for future large-scale optical satellite networks.

Cite

DOI 10.1109/wisee57913.2025.11229866

BibTeX

@inproceedings{DBLP:conf/wisee/GerardFC25,
  author    = {Jason Gerard and Juan A. Fraire and Sandra C{\'{e}}spedes},
  title     = {Modeling Pointing, Acquisition, and Tracking Delays in Free-Space Optical Satellite Networks},
  booktitle = {IEEE International Conference on Wireless for Space and Extreme Environments (WiSEE)},
  pages     = {1--6},
  publisher = {{IEEE}},
  year      = {2025},
  doi       = {10.1109/wisee57913.2025.11229866}
}

More on mega-constellations

Anyone, Anywhere, not Everyone, Everywhere: Starlink Doesn't End the Digital Divide Wesley Woo, Juan A. Fraire, Sylvia Ratnasamy, Scott Shenker, and Shaddi Hasan ACM Workshop on Hot Topics in Networks (HotNets), 2025
Abstract
Low Earth Orbit (LEO) satellite constellations, such as Starlink, are increasingly promoted as a solution to the digital divide in rural and underserved communities. In this paper, we take a closer look at the limits of this approach. Using the insight that capacity limitations of LEO-based access networks are driven by peak demand density, we introduce a simple analytical model that brings together real-world demand data with the physical and regulatory limits of LEO satellite networks. Applying our model to broadband demand across the United States, we find that serving the current Starlink constellation size is likely insufficient for covering all un- and underserved locations in the US and we find diminishing returns that disincentivize scaling the constellation to serve the long-tail of these un(der)served locations. We also identify that Starlink's current pricing is likely unaffordable for the majority of these locations, even with existing government subsidies. We argue that LEO constellations, while technologically impressive, are just another piece of the solution, rather than a panacea. New, innovative approaches are still required to end the digital divide.

HAL Publisher
On the Use of Mega Constellation Services in Space: Integrating LEO Platforms Into 6G Non-Terrestrial Networks Gabriel Maiolini Capez, Mauricio A. Cáceres, Roberto Armellin, Christopher P. Bridges, Juan A. Fraire, Stefan Frey, and Roberto Garello IEEE Journal on Selected Areas in Communications, 2024
Abstract
This paper presents a framework for integrating Low-Earth Orbit (LEO) platforms with Non-Terrestrial Networks (NTNs) in the emerging 6G communication landscape. Our work applies the Mega-Constellation Services in Space (MCSS) paradigm, leveraging LEO mega-constellations’ expansive coverage and capacity, designed initially for terrestrial devices, to serve platforms in lower LEO orbits. Results show that this approach overcomes the limitation of sporadic and time-bound satellite communication links, a challenge not fully resolved by available Ground Station Networks and Data Relay Systems. We contribute three key elements: (i) a detailed MCSS evaluation framework employing Monte Carlo simulations to assess space user links and distributions; (ii) a novel Space User Terminal (SUT) design optimized for MCSS, using different configurations and 5G New Radio Adaptive Coding and Modulation; (iii) extensive results demonstrating MCSS’s substantial improvement over existing Ground Station Networks and Data Relay Systems, motivating its role in the upcoming 6G NTNs. The space terminal, incorporating a multi-system, multi-orbit, and software-defined architecture, can handle Terabit-scale daily data volumes and minute-scale latencies. It offers a compact, power-efficient solution for properly integrating LEO platforms as space internet nodes.

HAL Publisher
RF-Assisted Uncertainty Cone Reduction in Free-Space Optical Inter-Satellite Links Elena Fernández-Niño, Juan A. Fraire, Adriano Camps, and Joan Adrià Ruiz-de-Azua IEEE Open Journal of the Communications Society, 2024
Abstract
One of the space communications industry’s current focuses is developing high-throughput communication terminals for satellite-to-satellite communication links. Optical inter-satellite links provide high data rates, long-range, and robustness against interferences, and they do not require frequency licensing as radiofrequency communication systems. Nevertheless, as the uncertain location of the receiver is comprised in an area larger than that illuminated by the transmitting laser, the pointing accuracy is a critical element in the success of the optical link establishment and maintenance, requiring a pointing, acquisition, and tracking mechanism. The acquisition process is the most time-consuming of the pointing processes, limiting the time available to send data, especially in highly dynamic networks. This paper focuses on reducing the acquisition time by reducing the initial satellite position uncertainty. To this end, a hybrid system that combines RF and optical technologies in a single communication module is proposed. Whereas the control plane is managed via the RF link to exchange more precise global navigation data, the optical link corresponds to the data plane in which payload data is exchanged. The pointing between two satellites is simulated to analyze its behavior, considering the error of cumulative orbital propagation data and global navigation satellite system data. This work also analyzes the cumulative error produced by the propagation of the TLEs over time. Finally, the results show how a system that relies on the exchange of global navigation satellite system positioning data achieves up to 99.45% better-pointing accuracy than a system that bases positioning data on TLE propagation.

HAL Publisher

Mega-constellations: the topic page All 33 papers on this topic