Global Navigation Satellite Systems Engineering, Policy, and Design
The gloves have come off now that test results show clearly the probable effects on GPS of LightSquared’s proposed wireless broadband network: widespread, debilitating interference to GPS receivers.
By Dee Ann Divis
FIGURE 1: Heading, bank and elevation angles of an actual platform carrying two perpendicular two meter-long baselines. The attitude solutions are shown for both the derived, or float, measurements (top), as well as the carrier phase-based, or fixed, measurements obtained after having correctly resolved the integer ambiguities (bottom). Precision differs between the methods by two orders of magnitude. Gray dots represent the two-dimensional projections on each of the three coordinate planes.Working Papers explore the technical and scientific themes that underpin GNSS programs and applications. This regular column is coordinated by Prof. Dr.-Ing. Günter Hein, head of Europe’s Galileo Operations and Evolution.
By Inside GNSS
Q: What is a virtual reference station and how does it work?
A: To reach centimeter-level — or even better — accuracy of positioning typically requires use of precise dual-frequency carrier phase observations. Furthermore, these observations are usually processed using a differential GNSS (DGNSS) algorithm, such as real time kinematic (RTK) or post-processing (PP). Regardless of the specific differential algorithm, however, implicit in the process is an assumption that the quality of the reference station data is consistent with the desired level of positioning accuracy.
By Inside GNSS
Washington View appears in each issue of Inside GNSS. It covers U.S. policy and program issues involving the Global Positioning System and other GNSSes. Reporting from Washington, D.C., columnist Dee Ann Divis has written about GNSS and the aerospace industry since the early 1990s in GPS World, Geo Info Systems, Jane’s International Defense Review, the Los Angeles Times, AeroSpace Daily and other publications.
By Dee Ann Divis
One of 12 magnetograms recorded at Greenwich Observatory during the Great Geomagnetic Storm of 1859
1996 soccer game in the Midwest, (Rick Dikeman image)
Nouméa ground station after the flood
A pencil and a coffee cup show the size of NASA’s teeny tiny PhoneSat
Bonus Hotspot: Naro Tartaruga AUV
Pacific lamprey spawning (photo by Jeremy Monroe, Fresh Waters Illustrated)
“Return of the Bucentaurn to the Molo on Ascension Day”, by (Giovanni Antonio Canal) Canaletto
The U.S. Naval Observatory Alternate Master Clock at 2nd Space Operations Squadron, Schriever AFB in Colorado. This photo was taken in January, 2006 during the addition of a leap second. The USNO master clocks control GPS timing. They are accurate to within one second every 20 million years (Satellites are so picky! Humans, on the other hand, just want to know if we’re too late for lunch) USAF photo by A1C Jason Ridder. 
Detail of Compass/ BeiDou2 system diagram
Hotspot 6: Beluga A300 600ST
1. DON’T BLAME GPS
Humboldt-Tolyabe National Forest, Nevada USA
√ In the Pacific Northwest, in-car navigators often indicate “short cuts” through wilderness mountains—with tragic results. One victim survived 49 days before rescue in May. (Reports blamed GPS – not digital maps or wireless communication.) GPS.GOV straightens out misperceptions, for those who need a guardian angel, but just get a signal.
Up here in the beautiful Pacific Northwest — yes, the sun is shining; hence, my enthusiasm — we have a wealth of wildlife. It goes nicely with the splendid landscape.
We have birds of all songs and colors. (Migratory Western tanagers passing through right now.) A selection of bears, mountain lions, the occasional wildcat. A surfeit of deer.
Even buffalo and grey wolves are making their comeback.
By Inside GNSS
Figure 1Q: How do you compute relative positions with GNSS?
A: GNSS is well recognized as an excellent means of computing position, but many people think that GPS only provides absolute position information. However, GNSS can also provide relative position information. In this column, we will look at some of the details of how this is done.
By Inside GNSS
After a long series of fits and starts, the Department of Homeland Security is tackling the issue of interference to the GPS signal. The agency has launched a study to assess the risks to GPS service from a variety of sources — a study that, at least on paper, will lead to a plan to mitigate interference.
Unfortunately, the effort will not directly address the one potential problem consuming the thoughts of the GPS community — widespread receiver overload from the high-powered mobile broadband service proposed by the Virginia firm LightSquared.
By Dee Ann Divis
Working Papers explore the technical and scientific themes that underpin GNSS programs and applications. This regular column is coordinated by Prof. Dr.-Ing. Günter Hein, head of Europe’s Galileo Operations and Evolution.
By Inside GNSS
One of 12 magnetograms recorded at Greenwich Observatory during the Great Geomagnetic Storm of 18591996 soccer game in the Midwest, (Rick Dikeman image)Nouméa ground station after the floodA pencil and a coffee cup show the size of NASA’s teeny tiny PhoneSatBonus Hotspot: Naro Tartaruga AUVPacific lamprey spawning (photo by Jeremy Monroe, Fresh Waters Illustrated)“Return of the Bucentaurn to the Molo on Ascension Day”, by (Giovanni Antonio Canal) CanalettoThe U.S. Naval Observatory Alternate Master Clock at 2nd Space Operations Squadron, Schriever AFB in Colorado. This photo was taken in January, 2006 during the addition of a leap second. The USNO master clocks control GPS timing. They are accurate to within one second every 20 million years (Satellites are so picky! Humans, on the other hand, just want to know if we’re too late for lunch) USAF photo by A1C Jason Ridder. Detail of Compass/ BeiDou2 system diagramHotspot 6: Beluga A300 600ST1. NORTHERN LIGHTS
Northern Hemisphere
√ The sun has been in a feisty mood lately, with solar flares mid-February to mid-March. GNSS signals haven’t been affected, because these plasma ejections have magnetic fields that are parallel to Earth, instead of perpendicular to it. That could change suddenly, according to the Space Weather Prediction Center. (Meanwhile, the Northern Hemisphere has enjoyed brilliant auroras.)
By Inside GNSS
Most of us who have ever gotten onto an airplane know the drill: when the doors are closed and sealed and the pilots push back from the terminal, the mobile phones are turned off — along with other portable electronic devices.
There’s a reason for that. Airline operators and the Federal Aviation Administration wish to avoid any possible interference with the aircraft’s avionics that support its navigation and communications functions.
By Dee Ann Divis
Q: Does the magnitude of the GNSS receiver clock offset matter?
A: It is well known that GNSS receiver clocks drift relative to the stable atomic time scale that ultimately defines a particular GNSS system in the first place. GNSS receiver manufacturers, however, try to limit the magnitude of the time offset to within some predefined range.
By Inside GNSS
For the complete story, including figures, graphs, and images, please download the PDF of the article, above.
Integer carrier-phase ambiguity resolution is the key to fast and high-precision GNSS positioning and navigation. It is the process of resolving the unknown cycle ambiguities of the carrier-phase data as integers. Once this has been done successfully, the very precise carrier-phase data will act as pseudorange data, thus making very precise positioning and navigation possible.
By Inside GNSS
