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High Accuracy-Nationwide Differential Global Positioning System Test and Analysis: Phase II Report

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Table of Contents

FOREWORD

The Nationwide Differential Global Positioning System (NDGPS) Modernization Program is a multiagency effort to examine the viability of long baseline carrier phase differential correction techniques. Phase I of this program analyzed the broadcast of GPS observables from a single NDGPS site, Hagerstown, MD, to aid in determining the appropriate signal structure and compression techniques to support long range carrier phase operations. In Phase II a second facility near Hawk Run, PA, was installed, enabling multiple baseline carrier and code phase navigation solutions.

This first report verifies the original accuracy achieved (10 cm, 95 percent horizontal) and addresses several additional research objectives such as the use of multiple reference stations to achieve even more accurate solutions.

Toni Wilbur
Director, Office of Operations Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

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SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

• Chapter 1-Introduction
  • Background
• Chapter 2-Phase II Task Reports
  • TASK 2: Collect, Process, and Report Information SIMULTANEOUSLY from the Hawk Run and Hagerstown Stations
  • TASK 3: Develop and Implement a Prebroadcast Integrity Algorithm
  • TASK 4: Develop Interface Software for Multiple Brands of GPS Receivers
  • TASK 5: Rewrite the Modulator Interface
  • TASK 6: Evaluate a Low Baud Rate Message and Processing
  • TASK 7: Collect Observations on One or More Highways in RTK Mode to Demonstrate Driver Analysis
  • TASK 8: Study Levels and Possible Noise Reduction at the Hagerstown Site
  • Summary

LIST OF FIGURES

• Figure 1. Map of South-Central PA showing Hawk Run, PA; Hagerstown, MD; and Orbisonia, PA. The latter test site is approximately 80 kilometers (km) from the reference stations.
• Figure 2. North component determined from HAG1 (black) and HRN2 (red), and the weighted average solution (green).
• Figure 3. East component determined from HAG1 (black) and HRN2 (red), and the weighted average solution (green).
• Figure 4. Height component determined from HAG1 (black) and HRN2 (red), and the weighted average solution (green).
• Figure 5. North component versus east component cross plot determined from HAG1.
• Figure 6. North component versus east component cross plot determined from HRN2.
• Figure 7. North component versus east component cross plot of HAG1 HRN2 combined.
• Figure 8. Antenna configuration on van used for collecting data broadcast from HAG1 and HRN2 simultaneously. The van is equipped with one GPS marine antenna and two demodulator receiver antennas.
• Figure 9. An example screen shot of prebroadcast positional integrity with the correct site coordinates.
• Figure 10. An example screen shot of prebroadcast positional integrity with the wrong coordinates.
• Figure 11. An example screen shot of prebroadcast measurement integrity. The four columns to the right show the difference between raw measurements and what is about to be broadcast. 16
• Figure 12. Demonstrated proof that GRIM to RTCM 18/19 works.
• Figure 13. Percentage of data collected 0 to 10 seconds for 25 epochs.
• Figure 14. Expected HA-NDGPS performance at 180 km.
• Figure 15. Comparing 5-second broadcast with 1-second broadcast from HAG1.
• Figure 16. Comparing 10-second broadcast with 1-second broadcast from HAG1.
• Figure 17. Comparing 15-second broadcast with 1-second broadcast from HAG1.
• Figure 18. Comparing 20-second broadcast with 1-second broadcast from HAG1.
• Figure 19. Map segment of test site along U.S. Route 15 north of Frederick, MD.
• Figure 20. Display of nine tracks driven on U.S. Route 15 north of Frederick, MD.
• Figure 21. Display of defined "road map" created from nine tracks in Figure 20.
• Figure 22. Representation of driver cross-track (i.e., left/right) driving variation for the 9 loops associated with figures 18 and 19.
• Figure 23. Van configuration used for driver analysis on U.S. Route 15.
• Figure 24. The Hagerstown GWEN site with a pentapod marine antenna 4 to 5 meters above the hut to search for the cleanest signals.
• Figure 25. Van configuration for multipath testing at the Hagerstown GWEN site for the NDGPS 700829 (3) antenna from Ashtech to van 700829 (3) antenna from Ashtech test.
• Figure 26. NDGPS 700829 (3) antenna from Ashtech to van 700829 (3) antenna from Ashtech initial convergence.
• Figure 27. NDGPS 700829 (3) antenna from Ashtech to van 700829 (3) antenna from Ashtech steady state with integers fixed.
• Figure 28. Van configuration used for multipath testing at the Hagerstown GWEN site. In this case, HA-NDGPS marine antenna to van marine antenna is under test.
• Figure 29. HA-NDGPS marine antenna to van marine antenna initial convergence.
• Figure 30. HA-NDGPS marine antenna to van marine antenna steady state with integers fixed.

LIST OF TABLES

• Table 1. Accuracy performance of 5-second broadcast scenario.
• Table 2. Accuracy performance of 10-second broadcast scenario.
• Table 3. Accuracy performance of 15-second broadcast scenario.
• Table 4. Accuracy performance of 20-second broadcast scenario.

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