The diversity and redundancy provided by multiple, independent, compatible, and in some respects, interoperable GNSS systems must be a good thing, right?
Well, almost certainly. But as with many things in life and technology, the devil’s in the details. And, as the varied characteristics and design specifications of new GNSSes and regional systems become clearer, it may not be too early to sort out those details.
Poll a representative cross-section of experts, and a consensus forms around the top three benefits of using signals from more than one GNSS: increased accuracy, integrity, and service availability — with continuity of service running a close fourth.
In challenging environments, such as urban areas, many signals are contaminated by non-line-of-sight reception or multipath interference. With multi-constellation GNSS, the best signals may be selected for a navigation solution and the worst ones discarded.
Moreover, multi-constellation GNSS brings a significant improvement in the proportion of space and time over which sufficient signals are available without interruption to compute a position solution.
Signal diversity and redundant measurements, together with better geometry from multiple GNSS satellites, allows improved receiver-based integrity monitoring to be carried out, including the detection of multiple satellite/signal failures.
These terms are equally applicable across all domains. For example, when sensing the atmosphere in order to estimate tropospheric delays (which feed into weather forecasting and climate-change studies), the increased number of signal rays through the atmosphere greatly improves the ability to refine the temporal and spatial density of the derived parameters and models.
Beyond this terra cognita, however, more systems bring more variables and more choices, and the way ahead is not always clear.
To help illuminate the unknowns, we called on not one expert, but rather a gallery of them from the iNsight Project — “Innovative Navigation using new GNSS SIGnals with Hybridised Technologies.” Four leading British academic GNSS research centers comprise iNsight.
Participants in this virtual roundtable included the following (with the initials by which they are identified in the answers to our questions): Professor Terry Moore (TM), Director of the Nottingham Geospatial Institute at the University of Nottingham; Professor Marek Ziebart (MZ), Head of the Space Geodesy and Navigation Research Group at University College London (UCL); Dr. Paul Groves (PG), a lecturer in the same group at UCL;Professor Washington Ochieng (WO), Director of the Imperial College London (ICL) Engineering Geomatics Group; Dr. Shaojun Feng (SF), an ICL research fellow; Professor Izzet Kale (IK), Director of the Applied DSP and VLSI Group at University of Westminster.