INNOVATION INSIGHTS with Richard Langley

Richard Langley

WE ARE ON THE BRINK OF A NEW ERA in satellite positioning and navigation. The excitement that was felt 30 years ago when the first GPS satellite was launched is beginning to be felt again. Back then, instantaneous three-dimensional satellite-based positioning was an entirely new concept. Yes, we did have satellite-based positioning before GPS, but it wasn't instantaneous and it wasn't fully 3D — nor was it very accurate.

Over the past 30 years, thousands of scientists and engineers have developed an amazing range of GPS applications providing positioning accuracies all the way down to the millimeter level. However, some would argue that many of the recent developments, especially in the area of high-accuracy positioning, are just minor enhancements to existing techniques first introduced or foretold years ago. Been there; done that.

But that situation is about to change — and in a big way! New signals and new satellites herald a new era in satellite-based positioning and navigation. Russia's Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) is being revitalized after many years of neglect. With its first launch in 1982, this second global navigation satellite system gave rise to the generic term for all such systems: GNSS. In addition to GLONASS and a modernized GPS featuring new civil and military signals along with new constellations of satellites, we will have Europe's Galileo system (with two GIOVE test satellites already in orbit) and China's Beidou/Compass system (with five satellites already in orbit). Receivers and data-processing techniques will be developed to allow use of all available signals and satellites. The future promises to be just as exciting for GNSS scientists and engineers as the early days of GPS.

But do we have to wait for these new or enhanced systems to be in place before benefiting from a multi-signal, multi-constellation global navigation satellite system? Definitely not. As this month's column describes, we can sample the future today. The existing GPS satellites, along with the revitalized GLONASS constellation and the satellites of the various geostationary satellite-based augmentation systems, already constitute a system of systems. And receivers currently on the market provide the necessary raw measurement data to yield positioning solutions from this system of systems with potentially more continuity and greater accuracy than those obtained using GPS alone. Listen up: the future is now.

"Innovation" is a regular column that features discussions about recent advances in GPS technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering at the University of New Brunswick, who welcomes your comments and topic ideas. To contact him, see the "Contributing Editors" section.

In the future, we will enjoy the benefits of a global navigation satellite system consisting of several independent systems. But do we have to wait for the future? No. The GNSS system of systems is already here. We have the extremely successful American GPS and the partly rebuilt Russian GLONASS, as well as several active geostationary satellite-based augmentation system (SBAS) satellites in orbit. All satellites of these three GNSSs provide us with ranging signals and thus pseudorange (code-phase) and carrier-phase observations usable for positioning and many other applications. This article focuses on the combined use of all readily available GNSS signals for precise positioning applications such as real-time kinematic (RTK) surveying operations, including carrier-phase ambiguity fixing.

This year, the GPS satellite constellation reached a new height: 31 active satellites in space and thus more GPS ranging signals available than ever before. But, for many applications, this still is not enough. As we all know from our own experiences, signals are often obstructed at many locations. More satellite signals can help increase GNSS availability. And more ranging signals improve positioning accuracy as well. Hence, the use of all available GNSS signals generally improves positioning performance.