GPS World

Tag: IOV

  • Galileo Achieves In-Orbit Validation

    Dual-frequency Galileo positioning performance during the In-Orbit Validation phase: positioning accuracy is an average 8 m horizontal and 9 m vertical (95% of the time). Its average timing accuracy is 10 nanoseconds on average. Plot courtesy of ESA.
    Dual-frequency Galileo positioning performance during the In-Orbit Validation phase: positioning accuracy is an average 8 m horizontal and 9 m vertical (95% of the time). Its average timing accuracy is 10 nanoseconds on average. Plot courtesy of ESA.

    The in-orbit validation of Galileo has been achieved, according to the European Space Agency (ESA). Europe now has the operational nucleus of its own satellite navigation constellation in place — the world’s first civil-owned and operated satnav system.

    Four is the minimum number of satellites needed to perform navigation fixes. In 2011 and 2012, the first four satellites were launched into orbit. In 2013, these satellites were combined with a growing global ground infrastructure to allow the project to undergo its crucial in-orbit validation phase: IOV.

    “IOV was required to demonstrate that the future performance that we want to meet when the system is deployed is effectively reachable,” said Sylvain Loddo, ESA’s Galileo Ground Segment manager. “It was an intermediate step with a reduced part of the system to effectively give evidence that we are on track.”

    Galileo Validated Video

    On March 12, 2013, Galileo’s space and ground infrastructure came together for the first time to perform the historic first determination of a ground location, taking place at ESA’s Navigation Laboratory in the ESTEC technical centre, in Noordwijk, the Netherlands. From that point, generation of navigation messages enabled full testing of the entire Galileo system. A wide variety of tests followed, carried out all across Europe.

    “ESA and our industrial partners had teams deployed in the field continuously for test operations,” said Marco Falcone, ESA’s Galileo System Manager. “More than 10,000 km were driven by test vehicles in the process of picking up signals, along with pedestrian and fixed receiver testing. Many terabytes of IOV data were gathered in all.”

    The single most important finding from the test results? Galileo works, and it works well. The entire self-sufficient system has been shown as capable of performing positioning fixes across the planet.

    Galileo’s observed dual-frequency positioning accuracy is an average of 8 meters horizontal and 9 meters vertical, 95 percent of the time. Its average timing accuracy is 10 billionths of a second. Its performance is expected to improve as more satellites are launched and ground stations come on line.

    For Galileo’s search and rescue function — operating as part of the existing international Cospas–Sarsat programme —  77 percent of simulated distress locations can be pinpointed within 2 kilometers, and 95 percent within 5 kilometers. All alerts are detected and forwarded to the Mission Control Centre within a minute and a half, compared to a design requirement of 10 minutes.

    “Europe has proven with IOV that in terms of performance we are at a par with the best international systems of navigation in the world,” said Didier Faivre, ESA director of Galileo and Navigation-related Activities.

    In an article for The System section of the February 2013 GPS World, Peter Steigenberger, Urs Hugentobler, and Oliver Montenbruck discuss Galileo-only positioning. “Using an ionosphere-free dual-frequency linear combination of pseudorange measurements on the Galileo E1 and E5a frequencies, the position of the TUME reference station [at the Technische Universität München (TUM) in Munich, Germany] could be determined with a 3D position error of less than 1.5 meters,’” the authors said. Read more here.

  • Galileo and Compass: A Tale of Also-Runnings

    Beating up the backstretch neck and neck, tied for third in the GNSS race, Galileo and Compass today offer some signals and some satellites to GNSS users — as long as those users are researchers. Galileo has more going for it in the way of signals, while Compass holds an edge in the number of satellites. Without an interface control document (ICD) to guide user/researchers and most importantly manufacturers in the employment of its signals, Compass satellites, however they may increase, are practically useless to anyone outside China. A Compass ICD has been rumored before and is now rumored again. Wait and see before placing your bets.

    The fourth Galileo in-orbit validation (IOV) satellite, Flight Model 4 (FM4), began transmitting signals on December 12, joining its co-launched confrère FM3, which began airing navigation signals on December 1. The FM4 spacecraft uses PRN code E20. As of this writing, FM3 is broadcasting E1, E5, and E6 signals, and FM4 is  broadcasting E1 and E5 signals; we don’t know if and when FM4 E6 signals start(ed) until ESA tells us.

    GPS World authors Oliver Montenbruck (German Space Operations Center) and Richard Langley (University of New Brunswick) have written an early analysis of the signals from FM3; this account will appear in the January issue of the magazine. A few selected excerpts from that article, and one figure:

    “Anyone with commonly available GNSS receivers can presently access the open signals in the E1, E5a, and E5b frequency bands as well as the wide-band E5 AltBOC signal.

    Source: GPS
    Figure 1: Pseudorange errors of IOV-3 tracking at Tanegashima, Japan, using the E1 BOC(1,1) signal (top) and the E5 AltBOC signal (center). The elevation angle over time is shown in the bottom panel.

    “According to an ESA statement, FM3will continue to use binary offset carrier modulation — specifically BOC(1,1) — on the E1 Open Service signals for the time being. In contrast to this, the first pair of IOV satellites has already started to use composite binary offset carrier modulation, which offers better multipath suppression in the received signal.

    “The E5 AltBOC pseudorange measurements in particular exhibit an exceptionally low noise and multipath level of better than 10 centimeters at mid- and high-elevation angles.”

    After discussing and displaying some carrier-phase measurements of the Galileo FM3 E1, E5, and E6 signals, Montenbruck and Langley conclude; “This level of performance highlights the potential benefit of Galileo signals in advanced triple-frequency techniques such as undifferenced ambiguity resolution and ionospheric monitoring.”

    Theoretically, the total of four Galileo IOV satellites now in medium-Earth orbit yield the minimum number needed to perform a 3D navigation fix, although no statement of initial — or even sketchy — operating capability has been issued by the European Space Agency (ESA), nor is one expected.

    Antonio Tajani, vice-president of the European Commission (EC) and head of the EC directorate-general responsible for industry and entrepreneurship, continues to publicly maintain a “political objective [of] the delivery of the first services before the end of 2014,” based on 18 orbiting satellites. In a December speech, he revised the basis for that position slightly to say the civil Open Service (OS) could be declared operational with as few as 12 satellites.

    The system operators had announced three dual-satellite launches in 2013, two dual-satellite launches and one four-satellite launch in 2014, hypothetically producing an operable constellation of 18 satellites by the end of the promised 2014. However, unconfirmed reports from Europe suggest that problems with manufacture of the next set of 14 Galileo satellites mean that no launches at all will take place until Q4 of 2013. Whether this will push out the service delivery date beyond 2014 or not remains open to conjecture.

    Compass

    Another matter open to conjecture and much speculation is whether the world will soon — or ever — see an interface control document (ICD) for China’s Compass system.  More than a year ago, I wrote that “The ICD has been rumored to be available previously to receiver manufacturers within China, creating some disgruntlement among companies outside the country . . .  GPS/Compass chips and receivers are being actively developed by many Chinese manufacturers and research institutes.”  Indeed, conference presentations, leading to a published article in this magazine’s October issue, “What Is Achievable with the Current Compass Constellation,“ confirm that this is so.

    And yet, the rest of the world neither has nor holds a Compass ICD.

    The end-of-year rumor mill has kicked into gear again, though. A GNSS industry representative stationed in Shanghai, China sent this message recently to a U.S. colleague: “Latest unofficial news said that the Compass Interface Control Document (ICD) will be released on 27th this month, and will be available on the internet on 28th.”

    We shall see what we shall see.