RTT-Based Localization of IoRT Nodes by a Single LEO Satellite: A Geometric Framework

This paper addresses the crucial challenge of geo-localization of ultra-low power Internet-of-Remote-Things (IoRT) devices placed in remote areas communicating directly with a Low Earth Orbit (LEO) satellite constellation. Accurate localization of IoRT devices is critical in various applications such as asset tracking, logistics, and environmental monitoring. Moreover, location information can also vastly support the employment of 3GPP-based standards for communication over satellite links. Location estimation of such ultra-low power and low-cost devices is only feasible on the satellite side. Use of Global Navigation Satellite System (GNSS) receivers at the IoRT terminals is not advised as they consume high power and add substantial computational complexity and cost. This paper proposes a novel geometric framework that enables the localization of static IoRT nodes on the satellite side using a single-antenna-equipped single LEO satellite. The proposed solution is based on the computation of the Round Trip Time (RTT) which can be used together with the prior available geometric parameters to compute the direct satellite-to-node distance and Angle-of-Arrival (AoA) parameters. Imprecision in RTT measurement translates into an error in the node localization. The error can be reduced by taking RTT measurements at multiple instances along the satellite's orbit, while minimum 2 measurements are required. A numerical analysis is conducted to prove the validity and usefulness of the proposed framework. The impact of the error in RTT measurements on the performance of the proposed localization scheme is also thoroughly investigated.