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Envisioning a Future GNSS System of Systems Günter W WORKING PAPERS Envisioning a Future GNSS System of Systems GÜNTER W. HEIN, JOSE ANGEL AvilA RODRIGUEZ, STEFAN WALLNER, BERND EISSFELLER, THOMAS PANY, AND PHILIPP HARTL Part 1 Russian Federal Space Agency/LockheedMartin/ESA Space Russian Federal Seven years ago, the U.S. Global Positioning System was the only real GNSS around. The GLONASS constellation had dwindled to seven satellites. Final approval and funding of Europe’s Galileo program was yet to be achieved. Since then, Russia has gone a long way toward rebuilding and modernizing GLONASS. Galileo has put its first experimental GNSS satellite, GIOVE-A, into space. And China has announced plans to build a full-fledged NG SS of its own — Compass — building on three Beidou satellites that it has launched in recent years. With those activities under way, it’s not too early to begin thinking about what a multisystem GNSS might look like and mean for users, receiver manufacturers, and service providers. e have just made the tran- era with the Global Positioning System Is it not time, therefore, to pause and sition into the new year of (GPS) as the result of efforts that began think for a moment about where we want 2007. Most of us probably in the late 1960s. The Russians followed GNSS to move? Is it not already time to Walready have our eyes focused soon afterwards (or did they do it in really “think global” and to coordinate onto the next 12 months along with parallel?) with GLONASS. Both of these and harmonize all the existing and pro- some wishes and perspectives that we systems are now undergoing extensive jected navigation satellite systems? If so, would like to have fulfilled in the com- modernization. Moreover, the European then the question naturally arises: what ing 365 days. Galileo system is joining the GNSS club, should the “Global Navigation Satellite In the same spirit, over the next two and China is now planning its own ver- System of Systems” look like? issues of Inside GNSS this column will sion called Compass. GPS | GALILEO | GLONASSThis column will try to shed some take a look into the near future and — In the meantime lots of augmenta- light on the fascinating new world of what is even more exciting — into the tion and regional systems have been GNSS in which we will live around the further future of satellite navigation. But developed or are currently under con- year 2020 if all the currently modern- what that future will look like depends sideration. From military to civil sig- izing and planned new systems come to an enormous extent on what the past nals, from medium Earth orbit (MEO) into reality. It will be a complex world was; so, we should have first a look back to geostationary Earth orbit (GEO) and where the word “coordination” will be into the roots of GNSS. inclined geosynchronous orbits (IGSO), the key and from which, if we do it right, Long ago the Americans entered the the palette of systems and offered ser- users will be the ones that will profit the global navigation satellite system (GNSS) vices is as wide as imagination allows. most. After all, why should a GNSS user 58 InsideGNSS JANUARY/FEBRUARY 2007 www.insidegnss.com WORKING PAPERS really care about whether one of his or U.S. Department of her signals comes from GPS, the other Defense. Although from Galileo, the third from GLONASS originally devel- and the fourth from Compass as long as oped for military the GNSS receiver works well? applications (we can also find some state- Scenes from the Present ments that GPS was Today only GPS is fully operational. intended to be a civil Nevertheless, Russia hopes to return as well as military GLONASS to full operation capability system from the very (FOC) with a completed constellation by beginning), the U.S. 2009, and Galileo’s FOC is now expected government made in 2012. Compass is already knocking GPS available to FIGURE 1 Launch history of GPS on the door, and in spite of the fact that civilians, transform- China has still a long way to go and ing it into the dual-use system it is today. of both civil and military users. To that lengthy negotiations will be needed, a Accordingly, certain signal capabilities objective the GPS Modernization plan scenario of four global coverage satel- are reserved for U.S. and allied military can be timely divided in the following lite systems seems to be very likely in a applications while the civilian signals are three blocks. future not so far away from today. open and free for worldwide use. Block IIR-M (replenishment-modern- From the experience with Gali- The GPS baseline constellation con- ized) satellites. This generation of space- leo, we know how important the roles sists of 24 satellites (21 + 3 active spares) craft introduced a second civil signal of interoperability and compatibility in six circular MEO planes at a nominal with improved services (L2C) reaching with GPS were from the very begin- average orbit semi-major axis of 26559.7 the 24-satellite FOC around 2012. Addi- ning. Unfortunately, major differ- kilometers with an inclination of the tionally, for military purposes the mod- ences between those two systems and orbital planes of 55 degrees with refer- ernized M-code — BOC(10,5) — will GLONASS still exist. ence to the equatorial plane. be placed on L1 and L2. Block IIR-M However, also on the GPS/GLONASS side, work on attaining real interoper- Is it not already time to really “think global” and ability is continuing. Just recently dur- to coordinate and harmonize all the existing and ing the GPS/GLONASS Working Group projected navigation satellite systems? 1 meeting in December 2006, both sides emphasized the benefit to the user com- munity that a common approach con- The first developmental satellites satellites also have antijam flex power cerning FDMA/CDMA would bring in were launched beginning in 1978, and capabilities for military needs. Figure terms of interoperability. The Russian the first operational satellites went into 4 provides more details on the signal side announced that they will come to orbit in 1989. The system reached initial structure. The first operational IIR-M a decision on adding or converting to a operational capability (IOC) in 1993 and satellite was launched on December 16, CDMA format by the end of 2007. The achieved FOC in 1995. The present GPS 2005. formal U.S.-Russia statement can be view constellation exceeds the baseline con- Block IIF (follow-on) satellites. The at < http://www.glonass-ianc.rsa.ru/i/ stellation with 30 orbiting satellites after third civil signal (L5) – BPSK(10) glonass/joint_statement_eng.pdf>. the last successful launch on November — begins with the IIF satellites. The The direction in which COMPASS 17, 2006. The history of all GPS launches FOC with 24 satellites is expected to be will go remains a large unknown. In can be seen in Figure 1. reached around 2015 fact, if the need of standardization was Block III. Still in the design phase, GPS always there, it seems that the concept GPS Modernization Block III includes prospective improve- is gaining in interest the more systems Before December 2005GPS the | basicGALILEO GPS | GLONASSments to both the ground and space come into play. capability consisted of the Standard segments. These will most likely include But before dreaming with our ideal Positioning Service (SPS) provided by increased anti-jam power, increased GNSS, let us first look more closely into the C/A-code on the L1 frequency and security, increased accuracy, navigation what the current reality is and what the the Precise Positioning Service (PPS) surety, backward compatibility, assured plans for new GNSS systems are. provided by the P(Y)-code on L1 and L2. availability, system survivability, and Although those services are of relatively controlled integrity — among other Global Positioning System good quality, the United States envis- improvements. The fourth civil signal GPS is made up of a network of initially aged modernizing the signals in order (L1C) will probably be introduced with 24 active satellites placed into orbit by the to improve the quality and protection this block. www.insidegnss.com JANUARY/FEBRUARY 2007 InsideGNSS 59 WORKING PAPERS 100 80 27 60 24 21 40 18 SV Number SV 15 Active Satellite 20 Decommisioned Satellite 12 9 0 6 3 Jan-92 Jan-94 Jan-82 Jan-84 Jan-02 Jan-04 Jan-96 Jan-86 Jan-90 Jan-98 Jan-06 Jan-88 Jan-00 0 Date 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 FIGURE 2 Launch history of GLONASS FIGURE 3 Plans to re-establish full operation capability of GLONASS In the 2004 GNSS cooperation agree- As can be seen in Figure 2, the cur- January 18, 2007, and in spite of the ment between the United States and the rent GLONASS status is far away from additional three recently launched sat- European Union (EU), the two parties its nominal numbers and as of Janu- ellites that should become operational, agreed to have BOC(1,1) as the baseline ary 18, 2007 only 9 active GLONASS the fulfilment of the GLONASS pro- waveform on both the GPS L1C and satellites were transmitting from gram objectives is still difficult. Galileo E1 Open Service (OS) signals. space. Seven additional space vehicles GLONASS Service Modernization. As Nevertheless, a group of experts from are on orbit but have been temporar- with GPS, GLONASS is on the way to Working Group A set up under the 2004 ily switched off and are currently not modernization of the system.
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