Direct-to-Cell: A First Look into Starlink's Direct Satellite-to-Device Radio Access Network through Crowdsourced Measurements (2506.00283v3)

Abstract: Low Earth Orbit (LEO) satellite mega-constellations have recently emerged as a viable access solution for broadband services in underserved areas. In 2024, Direct Satellite-to-Device (DS2D) communications, which enable unmodified smartphones to connect directly to spaceborne base stations, entered large-scale beta testing, with Starlink globally leading deployments. This paper presents the first measurement study of commercial DS2D services. Using crowdsourced mobile network data collected in the U.S. between October 2024 and April 2025, our research derives evidence-based insights into the capabilities, limitations, and prospective evolution of DS2D technologies providing Supplemental Coverage from Space (SCS) services to expand existing mobile network connectivity. We observe a strong correlation between the number of satellites deployed and the expanding extension of observed measurements, concentrated in accessible but poorly covered areas by terrestrial networks, such as national parks and large low-density counties. The data reveal stable physical-layer value measurement throughout the observation period, with a lower median RSRP (24-dB difference) and a higher RSRQ (3 dB difference) compared to terrestrial networks, reflecting the SMS-only usage of the DS2D network during this period. Based on SINR measurements, we estimate the expected performance of the announced DS2D mobile data service to be around 4 Mbps per beam in outdoor conditions. We also discuss strategies to expand this capacity up to 12 Mbps in the future, depending on key regulatory decisions regarding satellite licenses, spectrum availability, and allowable radiated power levels.

• The paper provides an empirical analysis of Starlink's Direct Satellite-to-Device (DS2D) network performance in early operation using crowdsourced LTE measurements from Android devices.
• Analysis shows a strong correlation between DS2D satellite launches and observed network expansion, with services primarily deployed in underserved geographic areas lacking terrestrial coverage.
• RAN performance metrics indicate lower RSRP but consistent RSRQ with lower loads, yielding a median SINR of 0 dB, with estimated current throughput around 4 Mbps per beam.

Overview of "Direct-to-Cell: A First Look into Starlink's Direct Satellite-to-Device Radio Access Network through Crowdsourced Measurements"

The paper "Direct-to-Cell: A First Look into Starlink's Direct Satellite-to-Device Radio Access Network through Crowdsourced Measurements" presents a seminal examination of Direct Satellite-to-Device (DS2D) communication networks, leveraging Starlink's infrastructure. This paper is particularly significant as it uses empirical data, specifically crowdsourced mobile network data, to evaluate the early operation phases of Starlink’s DS2D services across the United States. The analysis spans from October 2024 to April 2025, capturing a period of significant infrastructural and regulatory developments, and focuses on the system’s performance as a Supplemental Coverage from Space (SCS) network.

Methodology and Data Sources

The research employs a rich dataset consisting of LTE measurements collected from Android devices to evaluate network capabilities and limitations. These data are anonymized and cover various Radio Access Network (RAN) metrics such as RSRP, RSRQ, and SINR. Additionally, the paper incorporates external datasets including numbers of DS2D-capable satellite launches, T-Mobile's terrestrial coverage maps, and U.S. Census Bureau population data. The authors employ a method to estimate the relative intensity of DS2D service usage at the county level, linking it to areas characterized by limited terrestrial network coverage.

Key Findings

1. Correlation Between Deployments and Network Expansion: The paper finds a strong correlation between the number of DS2D satellites launched and the distinct cell identifiers observed through the collected data. This highlights the rapid expansion capability of Starlink’s constellation and proves the effectiveness of crowdsourced data in tracking such deployments.
2. Geographic Distribution of Service Use: Spatial analysis indicates a focused deployment of DS2D services in underserved areas, such as national parks and sparsely populated regions, where terrestrial infrastructure is often lacking. This trend underscores the service’s role in enhancing connectivity in remote areas, which is particularly critical during emergencies such as hurricanes and wildfires.
3. RAN Performance Metrics: The paper provides a detailed comparison of RSRP, RSRQ, and SINR between Starlink’s DS2D network and T-Mobile’s terrestrial LTE network. It is noted that the DS2D network exhibits lower RSRP but more consistent RSRQ with lower network loads, yielding a median SINR of 0 dB. These findings reflect the current SMS-limited usage of the service and the greater distances associated with satellite communication.
4. Estimated Network Performance: With present SINR levels, the DS2D network achieves a modest throughput estimated at 4 Mbps per beam. However, forthcoming increases in allowable radiated power could potentially enhance this to 11.7 Mbps, depending on regulatory developments and spectrum allocation.

Implications and Future Directions

The implications of these findings are far-reaching both theoretically and practically. Starlink’s DS2D can potentially transform mobile network planning strategies by providing an alternative or a complementary method for coverage in under-served regions. This approach also highlights potential regulatory and policy considerations, especially concerning spectrum allocation and interference management.

From a research perspective, the paper validates the utility of crowdsourced measurements as a reliable data source for evaluating large-scale deployments, which holds promise beyond mere technical evaluations and extends into policy and planning realms.

Future developments could witness enhanced DS2D performance through further constellation expansions and improvements in satellite antenna technologies. The scalability of such configurations will be closely watched, as they could redefine the landscape of global communication networks, particularly in the context of rural and disaster-stricken areas.

In conclusion, this paper provides a foundational examination of DS2D networks and sets the stage for continued research and development in satellite-based communications, potentially leading to a more connected and resilient global network infrastructure.