Skip to main content

Main menu

  • Home
  • Current Issue
  • Archive
  • About Us
    • About NAVIGATION
    • Editorial Board
    • Peer Review Statement
    • Open Access
  • More
    • Email Alerts
    • Info for Authors
    • Info for Subscribers
  • Other Publications
    • ion

User menu

  • My alerts

Search

  • Advanced search
NAVIGATION: Journal of the Institute of Navigation
  • Other Publications
    • ion
  • My alerts
NAVIGATION: Journal of the Institute of Navigation

Advanced Search

  • Home
  • Current Issue
  • Archive
  • About Us
    • About NAVIGATION
    • Editorial Board
    • Peer Review Statement
    • Open Access
  • More
    • Email Alerts
    • Info for Authors
    • Info for Subscribers
  • Follow ion on Twitter
  • Visit ion on Facebook
  • Follow ion on Instagram
  • Visit ion on YouTube
Research ArticleOriginal Article
Open Access

Precise Onboard Time Synchronization for LEO Satellites

Florian Kunzi and Oliver Montenbruck
NAVIGATION: Journal of the Institute of Navigation September 2022, 69 (3) navi.531; DOI: https://doi.org/10.33012/navi.531
Florian Kunzi
Deutsches Zentrum für Luft- und Raumfahrt (DLR), German Space Operations Center (GSOC), 82234 Weßling, Germany
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: [email protected]
Oliver Montenbruck
Deutsches Zentrum für Luft- und Raumfahrt (DLR), German Space Operations Center (GSOC), 82234 Weßling, Germany
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • Article
  • Figures & Data
  • Supplemental
  • References
  • Info & Metrics
  • PDF
Loading

Article Figures & Data

Figures

  • Tables
  • Additional Files
  • FIGURE 1
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 1

    USO time offset (top) and fractional frequency offset (center) over a 2-week period starting on January 17, 2021 show the USO’s frequency stability; occasional frequency jumps during SAA passes are illustrated by a zoomed-in version showing the fractional frequency offset for a 24-h interval (bottom).

  • FIGURE 2
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 2

    Flowchart of the orbit and clock determination algorithm; the receiver time trcv is predicted based on the time delta between the IMT beats b of two consecutive epochs as well as the last known fractional frequency offset Embedded Image. After the measurement update, the predicted time is corrected with the residual clock offset Embedded Image to form the best estimate Embedded Image of GPST at epoch i

  • FIGURE 3
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 3

    Real-time orbit estimation error compared to the POD solution in radial, along-track, and cross-track axes

  • FIGURE 4
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 4

    Difference of the GPST-aligned or GST-aligned receiver timescale with respect to the timescale of the CODE clock products

  • FIGURE 5
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 5

    Timescale estimation error with respect to CODE clock products using GPS and Galileo measurements (left) and corresponding ISB curves (right) for different ISB process noise settings; the negative broadcast GGTO is plotted as reference

  • FIGURE 6
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 6

    Time deviation of the estimated receiver time trcv relative to the reference clock product tCODE; the receiver time was estimated using an ISB process noise of σISB = 6 mm over 30 s as shown in the second row of Figure 5

  • FIGURE 7
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 7

    Carrier-phase residuals (post-measurement update) during an SAA pass at around 2 am on January 22 for a free clock estimation (top) and an over-constrained clock model

  • FIGURE 8
    • Download figure
    • Open in new tab
    • Download powerpoint
    FIGURE 8

    Distribution of the a-priori clock prediction error for Case 1 (free estimation, left), Case 2 (constrained, center), and Case 3 (over-constrained, right); the dashed blue line indicates a normal distribution for reference.

Tables

  • Figures
  • Additional Files
    • View popup
    TABLE 1

    Sentinel-6A General Properties

    ParameterValueUnit
    Mass11,186.6kg
    Dimensions5.1 × 2.3 × 2.6m3
    Semi-major axis7,714.4km
    Inclination66.0deg
    Orbital Period112.5min
    • ↵1 Approximate mass during evaluation period

    • View popup
    TABLE 2

    Timescale Naming Conventions

    AbbreviationDescription
    GPSTGPS system time
    GSTGalileo system time
    trcvTime in the local receiver timescale; the receiver timescale is realized through the oscillator of the GNSS receiver and a clock model that is continuously updated in the real-time navigation filter to minimize the difference between the receiver timescale and GPST or, alternatively, GST.
    tCODETime in the reference timescale of precise GNSS clock products of the Center for Orbit Determination in Europe (CODE); the CODE timescale is realized through a highly stable hydrogen maser clock and closely aligned to GPST.
    • View popup
    TABLE 3

    Estimation Parameters and GNSS Measurements used for Real-Time Processing

    ItemDescription
    Estimation
        FilterExtended Kalman filter
        Estimation parametersEpoch state vector, empirical accelerations, epoch-wise residual phase offset and fractional frequency offset, inter-system bias, phase ambiguities
        Stochastic modelsWhite observation noise, elevation-independent weighting, zero a-priori values, and configurable standard deviation of empirical accelerations
        AmbiguityFloat
    GNSS Measurements
        GNSS ObservationsUndifferenced GPS L1 C/A / L2C, L1/L2 P(Y), and Galileo E1/E5a pseudorange and carrier phase (Table 4)
        Sampling rate30 s
        GNSS data arcContinuous from January 17 to January 30, 2021; telemetry data gap on January 25 between 02:29 and 02:46
        GNSS satellite biasesGPS C1C/C2L timing group delay (TGD) and inter-signal corrections from CNAV; Galileo C1C/C5Q neglected
        Phase windupNeglected
        S6A GNSS antennaConstant antenna offset in satellite body frame; zero antenna phase center offset
        S6A attitudeQuaternions (measured)
        Reference frameGPS: WGS84(1762’) (Malys et al., 2016); Galileo: GTRF19v01
    Orbit Model
        Earth gravity fieldGOCO03S (Tapley et al., 2004) up to order and degree 50, rate terms Ċ20, Ċ21, Ṡ21
        Third-body gravityPoint-mass model; truncated analytical series of luni-solar coordinates (Montenbruck & Gill, 2000)
        Solid Earth tidesK2 tides (Rizos & Stolz, 1985)
        Ocean tidesNeglected
        RelativityNeglected
        Solar radiation pressureCannonball model
        Earth radiation pressureNeglected
        Atmospheric forcesCannonball model; Harris-Priester model for medium-solar flux (Harris & Priester, 1962)
        Empirical accelerationEpoch-wise approximation; three components in radial, tangential, normal direction; constant during propagation step
        Reference frameITRF
        Earth orientationGPS CNAV Earth Orientation Parameters (EOP; GPS ICD, 2020)
        Numerical integration4th-order Runge-Kutta
    • View popup
    TABLE 4

    GNSS Signal Combinations used in the EKF

    Constellation/BlockSignal CombinationRINEX ID
    GPS IIRL1 P(Y) + L2 P(Y)1W/2W
    GPS IIR-M, IIF, IIIL1 C/A + L2-CL1C/2L
    GalileoE1-C + E5-Q1C/5Q

Additional Files

  • Figures
  • Tables
  • Video Abstract

PreviousNext
Back to top

In this issue

NAVIGATION: Journal of the Institute of Navigation: 69 (3)
NAVIGATION: Journal of the Institute of Navigation
Vol. 69, Issue 3
Fall 2022
  • Table of Contents
  • Index by author
Print
Download PDF
Article Alerts
Sign In to Email Alerts with your Email Address
Email Article

Thank you for your interest in spreading the word on NAVIGATION: Journal of the Institute of Navigation.

NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. We do not capture any email address.

Enter multiple addresses on separate lines or separate them with commas.
Precise Onboard Time Synchronization for LEO Satellites
(Your Name) has sent you a message from NAVIGATION: Journal of the Institute of Navigation
(Your Name) thought you would like to see the NAVIGATION: Journal of the Institute of Navigation web site.
Citation Tools
Precise Onboard Time Synchronization for LEO Satellites
Florian Kunzi, Oliver Montenbruck
NAVIGATION: Journal of the Institute of Navigation Sep 2022, 69 (3) navi.531; DOI: 10.33012/navi.531

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Share
Precise Onboard Time Synchronization for LEO Satellites
Florian Kunzi, Oliver Montenbruck
NAVIGATION: Journal of the Institute of Navigation Sep 2022, 69 (3) navi.531; DOI: 10.33012/navi.531
Reddit logo Twitter logo Facebook logo Mendeley logo
  • Tweet Widget
  • Facebook Like
  • Google Plus One
Bookmark this article

Jump to section

  • Article
    • Abstract
    • 1 INTRODUCTION
    • 2 SENTINEL-6A
    • 3 METHODOLOGY
    • 4 RESULTS AND DISCUSSION
    • 5 SUMMARY AND CONCLUSION
    • HOW TO CITE THIS ARTICLE
    • REFERENCES
  • Figures & Data
  • Supplemental
  • References
  • Info & Metrics
  • PDF

Related Articles

  • Google Scholar

Cited By...

  • No citing articles found.
  • Google Scholar

More in this TOC Section

  • GPS Spoofing Mitigation and Timing Risk Analysis in Networked Phasor Measurement Units via Stochastic Reachability
  • A Consistent Regional Vertical Ionospheric Model and Application in PPP-RTK Under Sparse Networks
  • Real-Time Ionosphere Prediction Based on IGS Rapid Products Using Long Short-Term Memory Deep Learning
Show more Original Article

Similar Articles

Keywords

  • clock model
  • inter-system bias
  • time synchronization
  • ultra-stable oscillator

Unless otherwise noted, NAVIGATION content is licensed under a Creative Commons CC BY 4.0 License.

© 2023 The Institute of Navigation, Inc.

Powered by HighWire