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Session A5: Receivers for New Space-Based Sources

A Look at the Stars: Navigation with Multi-constellation LEO Satellite Signals of Opportunity – Starlink, OneWeb, Orbcomm, Iridium, and NOAA
Zak M. Kassas, The Ohio State University
Location: Ballroom C
Date/Time: Tuesday, Jun. 4, 8:55 a.m.

We are witnessing a renewed space race. From technology giants, to startups, to governments, everyone is claiming stake in launching their own LEO constellation. These constellations promise to transform our daily lives, offering broadband connectivity anywhere on Earth, and will benefit scientific inquiry in fields such as remote sensing. However, not all such constellations are created equal. So-called megconstellations comprising tens of thousands of satellites are on their way to become a reality, with SpaceX’s Starlink being the clear frontrunner with their plan to deploy nearly 12,000 LEO satellites. These constellations will be welcomed by current constellations inhabiting LEO, and collectively they could usher a new era for positioning, navigation, and timing (PNT).
The promise of utilizing LEO satellites for PNT has been the subject of extensive recent studies. These studies can be categorized into three groups. The first considers providing a standalone navigation solution by launching PNT-dedicated LEO constellations or transmitting PNT signals from existing LEO constellations. The second considers augmenting global navigation satellite systems (GNSS) with LEO constellations. The third exploits LEO signals from any constellation in an opportunistic fashion. LEO satellites possess desirable attributes for PNT: (i) they are around twenty times closer to the Earth compared to GNSS satellites, which reside in medium Earth orbit (MEO), which could yield significantly higher carrier-to-noise ratio; (ii) they are becoming abundant as tens of thousands of broadband Internet satellites are expected to be deployed into LEO; and (iii) they transmit in different frequency bands and are placed in varying orbits, making LEO satellite signals diverse in frequency and direction. However, exploiting LEO satellite signals for PNT purposes in an opportunistic fashion comes with challenges, as these constellations are owned by private operators that typically do not disclose crucial information about the satellites’: (i) ephemerides, (ii) clock synchronization and stability, and (iii) signal specifications. To address the first challenge, several approaches have been proposed, including differential navigation utilizing known base receiver(s), simultaneous tracking and navigation (STAN), and analytical/machine-learning satellite orbit tracking. Approaches to address the second challenge have been offered via adaptive interacting multiple model estimation. To address the third challenge, the paradigm of cognitive opportunistic navigation, which estimates the unknown LEO satellite signals in a blind fashion has been showing tremendous promise.
This presentation gives current state-of-the-art navigation results with multi-constellation LEO satellite signals of opportunity. First, a LEO cognitive receiver is presented, which could blindly acquire and track unknown LEO satellite signals to produce navigation observables: pseudorange, Doppler, and carrier phase. The receiver is agnostic to the modulation and multiple access scheme adopted by the satellite. The receiver’s efficacy is demonstrated by exploiting Starlink, OneWeb, Orbcomm, Iridium, and NOAA LEO satellite signals to localize a stationary receiver to an unprecedented level of accuracy. Starting with an initial estimate 3,600 km away from the receiver’s true position, a two-dimensional (2-D) positioning error of 5.1 m with signals from 4 Starlink, 2 OneWeb, 1 Iridium, 1 Orbcomm, and 1 NOAA LEO satellites. Next, a ground vehicle was equipped with an industrial-grade inertial measurement unit (IMU) and an altimeter. The vehicle traversed 4.15 km in 150 seconds (GNSS signals were only available for the first 2.33 km). By exploiting signals from 4 Starlink, 1 OneWeb, 2 Orbcomm, and 1 Iridium to aid the IMU via the STAN framework, the 3–D position RMSE and final 3-D error were 9.5 m and 4.4 m, respectively. These results represent the most accurate results published to-date with multi-constellation LEO satellites.

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