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IGS-MGEX Preparing the Ground for Multi-Constellation GNSS Science

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IGS-MGEX Preparing the Ground for Multi-Constellation GNSS Science IGS-MGEX Preparing the Ground for Multi-Constellation GNSS Science OLIVER MONTENBRUCK With four new and emerging constellations (BeiDou, Galileo, GERMAN AEROSPACE CENTER (DLR), GERMAN SPACE OPERATIONS CENTER (GSOC) QZSS, IRNSS) as well as the ongoing modernization of the PETER STEIGENBERGER U.S. Global Positioning System and Russia’s GLONASS, INSTITUTE FOR ASTRONOMICAL AND PHYSICAL the world of satellite navigation is undergoing dramatic GEODESY, TECHNISCHE UNIVERSITÄT MÜNCHEN ROBERT KHACHIKYAN changes. Facing these challenges, the International GNSS NASA JET PROPULSION LABORATORY/ Service has initiated the Multi-GNSS Experiment to enable INTERNATIONAL GNSS SERVICE CENTRAL BUREAU an early familiarization with the new systems and to prepare GEORG WEBER GERMAN FEDERAL AGENCY FOR CARTOGRAPHY their incorporation into high-precision GNSS modeling AND GEODESY and analysis. This article reports on the status of the new RICHARD B. LANGLEY constellations and the MGEX project and describes initial UNIVERSITY OF NEW BRUNSWICK, GEODESY AND GEOMATICS ENGINEERING data products and recent results for individual systems. LEOŠ MERVART TECHNICAL UNIVERSITY OF PRAGUE, FACULTY OF CIVIL ENGINEERING ver the past decade, the world These independent services are further URS HUGENTOBLER of global positioning has expe- complemented by a variety of satellite- INSTITUTE FOR ASTRONOMICAL AND PHYSICAL rienced dramatic changes. based augmentation systems (SBASs) GEODESY, TECHNISCHE UNIVERSITÄT MÜNCHEN O Starting from just a single con- to increase the availability, accuracy, stellation (GPS), a set of six global or and reliability of PNT for safety-critical regional navigation satellite systems — applications. with the addition of GLONASS, BeiDou, The potential merits of the new navi- GNSS monitoring station at the German Galileo, Quasi-Zenith Satellite System gation satellite systems have long been Antarctic Receiving Station (O’Higgins), (QZSS) and the Indian Regional Navi- praised and often been used to justify jointly operated by the Federal Agency for gation Satellite Systems (IRNSS) — has the need for their build-up. Leaving Cartography and Geodesy (BKG) and the emerged that are already offering, or at aside the political arguments for an German Aerospace Center (DLR) least preparing, a space-based position, independent national PNT infrastruc- navigation, and timing (PNT) service. ture, multi-constellation systems can 42 InsideGNSS JANUARY/FEBRUARY 2014 www.insidegnss.com indeed offer numerous advantages over ing Group. MGEX serves as a framework System Blocks Signals Sats stand-alone GPS navigation and the use for increasing the overall awareness of L1 C/A, L1/L2 IIA 8 of its legacy ranging signals. New signal multi-GNSS within the scientific and P(Y) structures will not only provide a greater engineering communities, as well as to L1 C/A, L1/L2 IIR-A/B 12 robustness against interference and mul- familiarize IGS participants and users GPS P(Y) tipath but also enable more robust track- with the new navigation satellite sys- IIR-M +L2C 7 ing at low signal levels. tems. The availability of unencrypted sig- This article will provide a brief over- IIF +L5 4 nals on three frequencies enables new view of new and modernized GNSS con- M L1/L2 C/A + P 24 GLONASS approaches to ambiguity resolution in stellations and their transmitted signals K +L3 (1) carrier-phase–based relative positioning as available in fall 2013. Thereafter, it GEO B1, B2, B3 5 and may also contribute to the analysis describes the MGEX network, which BeiDou IGSO B1, B2, B3 5 of higher-order ionospheric path delays. the IGS has established for multi-GNSS Last, but not least, the simple increase tracking and is operated in parallel to MEO B1, B2, B3 4 E1, (E6), in the number of available satellites not the legacy network in use for GPS and Galileo IOV (4) only enhances navigation applications, GLONASS. E5a/b/ab but also offer an increased number of A subsequent section presents ini- L1 C/A, L1C, signals for space weather applications tial MGEX data products, assesses their QZSS n/a SAIF 1 L2C, E6 LEX, L5 that employ occultation techniques and achieved performance, and discusses ray tracing of the neutral atmosphere relevant processing standards. We con- IRNSS n/a L5,S (1) and the ionosphere. clude with a discussion of necessary TABLE 1. Deployment status of global and regional Given the remarkable contributions steps and actions required in order to navigation satellite systems as of September to science that GPS continues to make fully incorporate new constellations and 2013. Satellites marked in brackets have not been declared operational. in geodesy, remote sensing, space, and signals into the IGS service portfolio. fundamental physics, similar and even larger benefits are commonly expected Navigation Satellite than the legacy signals. Upon full imple- from the new space-based PNT systems. Systems Status mentation in December 2014, CNAV Many of the cited applications make Table 1 summarizes current space-based signal accuracy should meet or exceed direct or indirect use of the Interna- PNT systems and operational satel- the legacy signals. tional GNSS Service (IGS), which has, lites as derived from the publication In addition to GPS and GLONASS, over many years, set the gold standard by R. Langley cited in the Additional the BeiDou system now offers a stand- for high-precision GPS and GLONASS Resources section near the end of this alone navigation service for the China measurement modeling and analysis. article. With the most recent launch of mainland and Asia-Pacific area, with a The IGS is a volunteer organization IRNSS-1A, a total of six navigation sat- global service expected to be available of more than 200 individual agencies ellite systems have so far become avail- by about 2020. Even though the BeiDou and institutions that maintain a global able. Among these, the legacy systems Open Service Interface Control Docu- network of monitoring stations and a GPS and GLONASS have long achieved ment (ICD) only covers the B1 and B2 long-term tracking data archive as well their full operational capability and pro- Open Service signals at present, signals as products derived from the analysis of vide navigation signals on at least two on up to three BeiDou frequencies can these measurements. frequencies (L1, L2) that can be accessed in fact be tracked by a variety of multi- With the advent of modernized GPS by civil users. GNSS receivers. BeiDou is thus the signals and the rise of numerous new The latest generations of GPS IIF first constellation enabling a systematic GNSS such as BeiDou, Galileo, QZSS, and GLONASS-K satellites have added assessment of triple-frequency position- and IRNSS as well as new augmenta- a third frequency (L5 and L3, respec- ing techniques. tion systems such as Russia’s System tively), but these signals remain limited Galileo presently has four in-orbit of Differential Correction and Moni- to a very small number of spacecraft. In validation (IOV) satellites in operation. toring (SCDM) and India’s GPS Aided June 2013, the GPS Directorate started These satellites support early testing and GEO Augmented Navigation (GAGAN) an initial test campaign with live broad- experimentation but have not yet been system, the IGS is fully committed to casts of the new L2C and L5 CNAV navi- declared healthy. An initial operational expand to a true multi-GNSS service. gation messages. These offer enhanced service with global coverage is targeted To pave the way for future provision navigation information and improved for a few years from now. Although of high-quality data and products for all positioning capabilities. The message- access to the Galileo E6 signals is still constellations, the IGS has initiated the populated broadcast is projected to not fully defined, users can freely access Multi-GNSS Experiment (MGEX) under begin April 2014. Users should expect signals with advanced multi-path per- coordination of its Multi-GNSS Work- initial CNAV signal accuracy to be less formance in the E1 and E5a/E5b bands. www.insidegnss.com JANUARY/FEBRUARY 2014 InsideGNSS 43 IGS-MGEX As a unique feature, the Galileo satel- stations has been lites are equipped with passive hydrogen deployed around masers. These offer exceptional clock the globe in paral- stability with many potential benefits lel to the legacy IGS for real-time navigation, precise posi- network for GPS tioning, and science applications. a nd GLONASS. Japan has validated the concept of Building on con- QZSS with its “Michibiki” satellite for tributions from more than two years. A fully operational various national QZSS comprising at least three satellites agencies, universi- in inclined geosynchronous orbit (IGSO) ties, and other vol- FIGURE 1 MGEX station distribution and supported constellations (as of and one in geostationary orbit (GEO), is unteer institutions, September 2013) envisaged within the present decade. the MGEX network QZSS supports a unique portfolio of had grown to almost 90 stations by Sep- cant challenge for consistent data pro- navigation signals on four distinct fre- tember 2013 (See Figure 1). cessing, this variety is, at the same time, quency bands and offers various types MGEX largely draws on the resourc- a valuable asset. The diversity of avail- of correction data for medium and high- es of institutions that have modernized able tracking techniques and types of accuracy users. their legacy GNSS monitoring net- data employed by the various receivers Finally, India launched a first satel- works in
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