Low Earth Orbit (LEO) satellite mega-constellations have emerged as a viable access solution for broadband connectivity in underserved areas. In 2024, Starlink, in partnership with T-Mobile, began beta testing an SMS-only Supplemental Coverage from Space (SCS) service. This marks the first large-scale deployment of Direct Satellite-to-Device (DS2D) communications, allowing unmodified smartphones to connect directly to spaceborne base stations. This paper presents the first measurement study of deployed DS2D technologies. Using crowdsourced mobile network data from the U.S. between October 2024 and July 2025, we provide evidence-based insights into the capabilities, limitations, and future evolution of DS2D technologies for extending mobile connectivity. We find a strong correlation between the number of satellites deployed, the number of unique cell identifiers measured, and the volume of measurements, concentrated in accessible areas with poor terrestrial network coverage, such as national parks and sparsely populated counties. Stable physical-layer measurements were observed throughout the period, with a 24-dB lower median RSRP and a 3-dB higher RSRQ compared to terrestrial networks, reflecting the SMS-only usage of the DS2D network during this period. Based on the SINR measurements collected, we estimate the expected performance of the announced DS2D mobile data service to be around 3 Mbps per beam in outdoor conditions. We also discuss strategies to expand this capacity up to 18 Mbps in the future, depending on key regulatory and business decisions, including allowable out-of-band emissions, permitted number of satellites, and availability of spectrum and orbital resources.

翻译：低地球轨道（LEO）卫星巨型星座已成为服务欠缺地区宽带连接的一种可行接入解决方案。2024年，星链（Starlink）与T-Mobile合作，开始测试一项仅支持短信的太空补充覆盖（SCS）服务。这标志着直连卫星至设备（DS2D）通信首次大规模部署，允许未经改装的智能手机直接连接到星载基站。本文首次对已部署的DS2D技术进行了测量研究。利用2024年10月至2025年7月期间来自美国的众包移动网络数据，我们为扩展移动连接的DS2D技术的能力、局限性和未来演进提供了基于证据的见解。我们发现，部署的卫星数量、测量到的唯一小区标识符数量以及测量数据量之间存在强相关性，这些活动集中在国家公园和人口稀少县等地面网络覆盖较差但可访问的区域。在整个观测期间，物理层测量结果保持稳定，其中位RSRP比地面网络低24 dB，RSRQ则高3 dB，这反映了此期间DS2D网络仅用于短信服务。基于收集到的SINR测量数据，我们估计已公布的DS2D移动数据服务在室外条件下的预期性能约为每波束3 Mbps。我们还讨论了未来将此容量提升至18 Mbps的策略，这取决于关键的监管和商业决策，包括允许的带外发射、许可的卫星数量以及频谱和轨道资源的可用性。