StarFire™ GNSS: The Next Generation StarFire Global Satellite Based Augmentation System Chaochao Wang and Ronald Hatch NavCom Technology, Inc. ABSTRACT StarFire receiver hardware and software. NavCom Technology has made numerous advancements in NavCom’s next generation StarFire GNSS system Satellite Based Augmentation Systems (SBAS) over performance is described in this paper. The StarFire the past 15 years and has continued to improve GNSS system is a Global Satellite Based receiver performance to a customer base that now Augmentation System (GSBAS) developed entirely consists of multiple thousands of users. The first by NavCom Technology. Significant improvements StarFire Wide Area Differential GPS correction have been made to each component of the system service, originally named Wide Area Correction including the ground reference network, new Transform (WCT), was introduced by NavCom in proprietary real-time orbit and clock generation, dual 1998. Like the current system it used dual- redundant delivery of corrections via commercial frequency GPS measurements for navigation and communication satellites, and the GNSS receiver precise point positioning. This continental WADGPS navigation software. Among the most significant StarFire system delivered better than 30cm position improvements is the incorporation of orbit and clock accuracy for users in North America. corrections for GLONASS satellites. At the same time, the orbital and clock correction accuracy for In 2002, NavCom introduced a truly global StarFire GPS satellites has been dramatically improved and GPS augmentation service. Using a global reference the receiver navigation software has been modified receiver network and an enhanced version of the to take advantage of both the GLONASS satellites Real-Time GIPSY (RTG) clock and orbital correction and the improved orbit and clock accuracy for GPS. software licensed from Jet Propulsion Lab (JPL), Each component of the StarFire GNSS system is corrections are generated for all of the GPS described below and the improved performance is satellites at two independent processing centers. compared to that of the legacy StarFire GPS (only) The StarFire clock and orbital corrections are system and is illustrated with comparative test currently uplinked to six geo-stationary satellites and results. broadcast from them to the user receivers. NavCom GPS receivers are able to use the StarFire GPS INTRODUCTION service to achieve better than 10cm RMS accuracy for a variety of applications. A diagram of the system NavCom Technology recently launched their next operation is shown in Figure 1. generation StarFire GNSS system, which enables current models of NavCom StarFire receivers to The recently introduced next generation StarFire achieve sub-decimeter navigation accuracy using GNSS augmentation service offers the following both the U.S. Global Positioning System (GPS) and enhancements and new capabilities: the Russian GLONASS system. StarFire provides 1. Reference Site Updates - The global global Precise Point Positioning (PPP) capability for various applications, such as precision farming, land reference receiver network used in the new survey, machine control, aerial navigation, and StarFire GNSS system is wholly owned and marine survey. The StarFire GNSS system includes operated by NavCom Technology. This NavCom’s Global Navigation Satellite System homogenous StarFire reference receiver (GNSS) reference receiver network, communication network enables NavCom to provide higher infrastructure, data collection system, network data system reliability and to modify and improve processing to compute precise clock and orbit the satellite correction accuracy. corrections, real-time correction distribution, and the Copyright © 2012 NavCom Technology, Inc. 2. Clock & Orbit Innovation - The data center software, which generates the clock and orbit corrections for the StarFire GNSS system, now uses NavCom developed proprietary software. This software incorporates innovative clock and orbit real- time estimation algorithms. This hub processing software produces 4 cm clock corrections for GPS satellites and 13 cm clock corrections for GLONASS satellites. Figure 1: StarFire overview As far as we can determine, the orbit and STARFIRE GNSS NETWORK clock corrections which we generate are In the new StarFire GNSS system, both GPS and competitive with the orbit and clock accuracy GLONASS range measurements are provided by formed by the International GNSS Service the newly deployed global reference receiver (IGS) from a weighted average of orbits and network. In this network NavCom SF-3050 receivers clocks generated by from 8 to 10 academic are collocated at each reference site to provide institutions and international government system redundancy. All of the GNSS data collected agencies. at these sites is transmitted back to geographically separated and independent StarFire processing 3. Expanded Rover Performance - With the centers in real-time. An additional StarFire receiver StarFire GNSS service, the NavCom is used to monitor the signal strength of the StarFire StarFire receivers use both GPS and L-band signal, as well as, the positioning GLONASS satellites for precise navigation. performance of the StarFire system at each The system availability, accuracy, and reference site. There are StarFire GNSS reference reliability of the navigation performance of sites strategically located on every continent other than Antarctica. This allows each GNSS satellite to StarFire receivers have been significantly be tracked by at least five or more reference sites improved. simultaneously. 4. Legacy StarFire GPS Operation - The STARFIRE GNSS CLOCK AND ORBIT StarFire system continues to broadcast the ESTIMATION StarFire GPS service (pre-April 2011) along The core technology used in the StarFire GNSS with the new StarFire GNSS service to system is NavCom’s innovative real-time GNSS maintain compatibility with legacy receivers. satellite clock and orbit computation engine. This NavCom Sapphire based receivers running state-of-art software computes and predicts the orbit the latest firmware are able to compute and clock of GNSS satellites in real-time using the position solutions using either the new raw GNSS measurements from NavCom’s global reference receiver network. This software can GNSS service or the older GPS service. determine the satellite orbit with an accuracy of 5cm This provides increased reliability and (1-sigma) for GPS and 14 cm (1-sigma) for inherent receiver redundancy. GLONASS satellites in real-time. Figure 2 shows a typical 24-hour real-time orbit error In short, the StarFire GNSS system is not merely a plot. This particular graph using, data obtained on simple step to include GLONASS satellites into the th April 9 , 2010, was generated by taking the final existing StarFire GPS system. Instead, it is a orbit product from the International GNSS Service revolutionary upgrade to the entire StarFire system, (IGS) as truth reference. There were 29 GPS and 16 including new reference sites and processing GLONASS satellites available at that time and the software. Each component of the system is average orbit accuracy was 3.96 cm for all GPS described below. satellites and 8.69 cm for all GLONASS satellites. This compares to the 17 cm typical orbit accuracy of the StarFire GPS service. Thus, the new StarFire GNSS corrections have been significantly improved. The new clock and orbit software is designed to expand gracefully as future constellations, such as Copyright © 2012 NavCom Technology, Inc. Galileo and/or COMPASS satellite systems become The two StarFire receivers shared a standard available. NavCom GNSS rover antenna and they were exposed to the same multipath conditions. In this GPS PRNS RMS H= 0.0227(m) C= 0.0203(m) L= 0.0252(m) 2D= 0.0324(m) 3D= 0.0396(m) versus IGS GPS PRNS MEAN H= 0.0047(m) C= 0.0024(m) L= 0.0034(m) 68% 3DRMS = 0.0411(m) 95% = 0.0674(m) setup, one of the receivers navigated using the 0.15 ) H m ( C StarFire GNSS service, while the other navigated S L M 0.1 R 3D r o r r using the legacy StarFire GPS service. The results E L C 0.05 H t show that the new StarFire GNSS solutions had i b r O 0 much smaller temporal variation over a 24-hr period 01 03 05 07 09 11 13 15 17 19 21 23 25 27 29 31 ALL GPS PRN ORBIT_EST_SAT_STAT0.DAT after convergence. In addition, the bias observed in GLN PRNS RMS H= 0.0302(m) C= 0.0506(m) L= 0.0639(m) 2D= 0.0815(m) 3D= 0.0869(m) versus IGS GLN PRNS MEAN H= 0.0032(m) C=-0.0232(m) L=-0.0010(m) 68% 3DRMS = 0.0912(m) 95% = 0.1475(m) StarFire GPS height solutions did not exist in H ) C m StarFire GNSS solutions. ( L S M R 0.1 3D r o r r E L C Table 1 shows the position error statistics of StarFire H t i b r 0.05 O N L GNSS navigation for these sample results. The RMS G 0 errors of the local level frame from the surveyed 01 03 05 07 09 11 13 15 17 19 21 23 ALL GLONASS PRN ORBIT_EST_SAT_STAT0.DAT position are: East 2.16 cm; North 2.22 cm; and Up 6.78 cm. The corresponding numbers of the legacy H – height in radial direction; C- cross track; L - along track StarFire GPS are: East 6.57 cm; North 6.80 cm; and Figure 2: StarFire GNSS orbit accuracy for GPS Up 17.44 cm, which were obtained with the same and GLONASS satellites hardware in identical signal conditions. This constitutes a three to one improvement in the horizontal accuracy and almost the same in the STARFIRE GNSS NAVIGATION WITH STARFIRE height. Figure 4 shows the number of satellites used GNSS CORRECTIONS in both StarFire modes. It is clear that the PDOP NavCom’s receiver navigation software has been (Position Dilution of Precision) using the StarFire upgraded to make optimum use of the newly GNSS navigation was always below 2 when aided introduced StarFire GNSS service. The receiver by the extra GLONASS satellites.