Multi-GNSS is making GNSS PNT commonplace

Sep 2019 | No Comment

Chris Rizos

Chris Rizos is an Emeritus Professor in the School of Civil and Environmental Engineering and a co-director of the Satellite Navigation and Positioning (SNAP) Lab at UNSW. Chris is president-elect of the International Union of Geodesy & Geophysics (IUGG).
Professor Rizos’ early fascination with old maps and Australia’s exploring pioneers sparked his own exploration of what we know today as the global navigation satellite technologies of the future. His research in Global Navigation Satellite Systems (GNSS), and their applications extends across the whole spectrum of uses from Navigation to Geodesy. With over 20 years of service to some of the most prominent international geodetic organisations, he has had the opportunity to be part of the evolution of a field that has considerable global impact.
As a big picture thinker he has watched Geodesy rapidly evolve with its tools and datasets helping geoscientists monitor global change (including natural and climate change), changes in the environment (to ice sheets and atmosphere) and geohazards (volcanos and earthquakes), and surveyors and engineers applying these technologies from small-scale building works to international mapping projects. Through his research, Professor Rizos’ aims to “spatially enable” all aspects of life, through the further development of technologies and systems that provide continuous, seamless, high accuracy positioning of objects, people and every feature on the surface of the Earth.

You have been active in international scientific unions, such as the IAG, and most recently you have been elected Vice President of the IUGG. Can you explain some of the activities of these organisations?

The international Union of Geodesy & Geophysics (IUGG –, is the umbrella organisation for many of the geoscience disciplines which are organised as 8 Associations. The IUGG was established on the 28 July 1919, and recently celebrated its 100 year anniversary in Paris at UNESCO Headquarters ( I have been elected Vice President for 4 years (2019-2023). The President is Professor Kathryn Whaller (Professor of Geophysics, University of Edinburgh), the first woman to hold this position.

As you can see from the Mission of the IUGG on its home page:

“The International Union of Geodesy and Geophysics (IUGG) is the international organization dedicated to advancing, promoting, and communicating knowledge of the Earth system, its space environment, and the dynamical processes causing change. Through its constituent Associations, Commissions, and services, IUGG convenes international assemblies and workshops, undertakes research, assembles observations, gains insights, coordinates activities, liaises with other scientific bodies, plays an advocacy role, contributes to education, and works to expand capabilities and participation worldwide.”

▪ The 8 IUGG Associations (in alphabetical order) are:

▪ IACS (international Association of Cryospheric Sciences)

▪ IAG (Int. Assoc. of Geodesy)

▪ IAGA (Int. Assoc. of Geomagnetism & Aeronomy)

▪ IAHS (Int. Assoc. of Hydrological Sciences)

▪ IAMAS (Int. Assoc. of Meteorology & Atmospheric Sciences)

▪ IAPSO (Int. Assoc. for the Physical Sciences of the Ocean)

▪ IASPEI (Int. Assoc. Seismology & Physics of the Earth’s Interior)

▪ IAVCEI (Int. Assoc. of Volcanology & Chemistry of the Earth’s Interior)

Each Association operates in a semi-autonomous fashion, running their own conferences, programs, outreach, services, etc. Increasingly, however, the need for multidisciplinary approaches to geoscience means that the associations are cooperating and running joint working groups or commissions, supporting combined conferences, etc. This trend is expected to continue. Having said that, it is also true that all geoscience disciplines now use geodetic technologies (to varying extents), such as GNSS, gravity fi eld mapping, InSAR, satellite altimetry, earth observation. Hence geodesy is increasing its “visibility” within the geosciences.

I was the IAG president for the period 2011-2015.

This is a world of multi-GNSS systems. What advantages do you see about this scenario?

The obvious advantages of multi-GNSS are related to measurements, signals and outputs. For example:

▪ More satellites increases redundancy and availability of signals, and increases precision of positioning results

▪ Multi-GNSS increases the number of signals, and hence increases robustness against jamming, etc.

▪ Multi-GNSS creates an environment of “friendly competition”, whereby advances in signal design and capabilities are evident, hence increasing accuracy and reliability of positioning results

Other commentators may also suggest that there is increased “choice” in which constellations and signals may be tracked. However I believe that the manufacturers of systems & developers of services for professional (high accuracy) users will want to make measurements on ALL open signals from ALL GNSS (& RNSS) constellations. Interestingly, a similar trend is evident for mass market users (via smartphone devices), in that GNSS chips are now (& increasingly so) tracking ALL GNSS (& RNSS) constellations, but only on 2 frequencies: L1 and L5.

Having said that, there must be a optimal number of GNSS/RNSS/SBAS satellites that provide all the above advantages, but beyond which the “law of diminishing returns” comes into play. There is no agreed-to number, but in my opinion we have enough GNSS constellations, and probably hitting the limit of RNSS and SBAS constellations.

Many countries plan GNSS systems primarily because of defense and security needs. Do you think that this may trigger a race with more countries joining in? What would be the implications?

Following from my remarks above, I believe that it would be counter productive (not to mention wasteful) for more GNSS to be developed. We already have plans (or hints) that RNSS & SBAS will increase in the near future, with systems from Korea, Australia and Brazil, and perhaps Nigeria being added to these base constellations. All GNSS, apart from Galileo, are primarily funded for defence and security needs (although we could argue that Galileo’s PRS is to some extent “militarised”). Some security component will no doubt be incorporated into ALL RNSS systems (e.g. so-called “restricted” or “authorised” signals). SBAS is a more complicated matter, as these “augment” the GNSS satellites, through provision of extra ranging signals and downlinks for augmented (accuracy and/or integrity) services to address only civilian applications.

I do predict that there will be a rush to develop “next generation” SBAS systems by many countries, as a means of delivering augmented PNT services to their nations (beyond aviation services). But I cannot rule out the possibility that even these will be ultimately outnumbered by systems launched and operated by private sector players. In fact, SBAS may evolve into systems that include (or be replaced by) downlink services from small, inexpensive LEO satellites (that do not require complex and expensive satellite clocks for GNSS signal generation).

How serious are the threats like interference, jamming and spoofing? How prepared is the GNSS community to deal with it?

Very serious! A day does not pass that we do not hear about jamming (and increasingly also spoofing) of user systems in localised areas. A few years ago we thought the threat was “misguided” individuals buying “privacy protection devices” from the internet, that jam GNSS at or near their truck, place of work, or home, in order to guard against unwanted (location) surveillance (where PNT or smartphone devices send coordinates to servers).

Though this is indeed a threat, it has not yet reached the predicted epidemic proportions. However, “state players” such as North Korea, Russia, Iran (& probably many other countries) have been denying PNT across large areas, impacting mostly (currently) the aviation and marine user communities. E-warfare is of course what every country’s military is gearing up as a capability to prosecute, and that means using means to deny GNSS capability to adversaries while somehow protecting their own capability. So there are no “bad guys” versus “good guys” in this respect. When President Trump visits another country, I suspect that there are localised GNSS jammers around his motorcade, just as is the case for Putin and Xi.

Spoofing is a more serious issue, as it is not a case of “GNSS denial of service” as in the case of jamming, but that it can result in seriously erroneous PNT results. Many instances of this have been identified, so this is no longer just a possibility, but a reality. Smarter receiver design, as well as some innovations in signals to protect against cyber attack, can go a long way to protect against spoofing. But currently we are a long way from these protective measures being implemented.

There have been a number of studies (and reports) on the impact of denial of GNSS service to society.

Thankfully, in “normal circumstances” (i.e. not a major nation-to-nation confl ict) any such denial would be short-term, and relatively localised. Nevertheless we need, at the very least, detection systems that can alert users to jamming or anomalous GNSS operations. The recent 6 day Galileo outage was not caused by “nefarious players”. Details of what did fail are not yet available. However, its outage did not impact users, as their receivers were able to continue to perform to specifi cations using measurements from the other GNSS/ RNSS constellations. This reinforces (though does not entirely support) the notion that it is extremely unlikely that ALL GNSS can simultaneously experience an outage.

Jamming or spoofing of autonomous systems is of course the nightmare scenario. So we do need back-up technologies.

Given this, what’s your opinion on GNSS back ups?

Unfortunately there is no alternative (non-GNSS) PNT (APNT) technology that simultaneously satisfies requirements such as low cost, low complexity, minimal infrastructure needs, wide/global coverage, adequate accuracy, high reliability & versatility.

Multi-GNSS is therefore seen as the ultimate “backup” because it is assumed that not all GNSS/ RNSS/SBAS signals and measurements will be denied to users for anything longer than perhaps a few hours. (But surely the most sophisticated GNSS denial will be using military-style e-warfare techniques, and we are seeing their effectiveness in the middle east and in baltic areas.)

There are some back-up options which have widespread applicability (not just global coverage, but also indoors), and most widespread is wifi -based positioning. But this is a relatively low accuracy positioning technology. With respect to navigation (especially autonomous systems), the solution is multi-sensor integration. In vehicles especially, GNSS may not even be considered essential for safety applications. As vision, Lidar and radar systems are better at “collision avoidance”. Developments such as “clock-on-a-chip” can address the timing requirements of modern societies. New high-performance INS are likely to come down in cost and size over the coming decades, and may be used for more than just a back-up for GNSS.

Then there are the bespoke systems, such as high accuracy PNT technologies that operate where GNSS cannot operate reliably, such as indoors or in high multipath environments. Locata is one such example. However they cannot be considered back-ups, as they are expensive, deployed in “hot spot” mode, and due to them being based on terrestrial ranging signals, are able to provide coverage only over relatively localised areas.

You also worked on Locata terrestrial positioning system. Can you explain the signifi cance of this system?

Locata is a high accuracy (centimetre-level) APNT technology based on terrestrial signals that are in many respects similar to GNSS signals. However the signals are transmitted in the non-licensed ISM 2.4GHz frequency band. Locata does have several innovative features that explain its high accuracy without the use of atomic clocks. However, in the short-to-medium term, there is no low-cost Locata receiver chip, and hence it remains only suitable for niche (and high-value) applications such as autonomous vehicles in ports and open-cut mines. In the coming years Locata could be integrated into GNSS receivers intended for high-value professional markets.

Whats is your take on eLoran?

As a back-up its only advantage is wide area coverage (assuming there are transmitter towers), and relatively low-complexity (resulting in low-cost receiver solutions). Its accuracy is very poor (both in respect to timing and positioning), and would hardly be a true back-up except for some very specific marine and air applications (where wifi -based positioning cannot be used). I would rather see efforts made to test the “scaling up” of other PNT technologies across cities and later across provinces and states, such as Locata (and its competitors), as their accuracy is more comparable to GNSS than eLoran.

What influences you envisage in satellite navigation in the near future given the advancements in the field of AI, Autonomous Vehicles, UAV, etc.?

Advances such as those listed will impact users and applications. In general they will expand “automation”, and in many instances increased automation (i.e. autonomous driving and transportation, automated mining, agriculture and construction, etc) will increase the need for PNT capabilities. Furthermore there will be increased demand for augmentation services, such as increased accuracy and increased integrity. As we mentioned above, such developments will drive the development of improved alternative PNT (APNT) technologies. Hence GNSS will become more important for the “digital transformation” revolution, in which AI, Big Data, 5G comms, UAVs, and automated systems all play their part. There is no doubt that without these requirements GNSS (and other PNT technologies) would remain a technology for primarily the professional markets, with its mass market use limited to LBS-smartphone applications (which have rather low performance requirements for GNSS-provided PNT results).

Geodesy has been an area where you have been very active. Do you think that Geodesy needs more attention as we do not find many Geodesists around?

Good question. Geodesy is becoming increasingly recognised as a vital component of what we might refer to as the Positioning Infrastructure, which underpins GNSS products and services (especially the augmented accuracy services).

Geodesy is responsible for the reference frame in which high accuracy positioning is expressed. Geodesy also provides the basic services and infrastructure (national and international) that support high accuracy GNSS positioning. Hence geodesy is becoming more closely associated with all aspects of the geospatial disciplines, from positioning (3D, heights, etc) through to mapping (in 3D and 4D). This is a welcome development. (Another example is the UN resolution on the Global Geodetic Reference Frame – GGRF – championed by the UN-GGIM Committee of Experts.)

Geodesy is also increasingly providing the tools, services and infrastructure to support (geo)science. As indicated earlier, the visibility of the IAG (and hence geodesy) within the IUGG (its other 7 Associations) is much higher than it was a decade ago. For example, we now have new initiatives within the IUGG in “seismo-geodesy” and “volcano-geodesy”.

Every discipline of science and engineering claims there is a shortage of qualifi ed practitioners and researchers. Geodesy (and even surveying) is no exception. But where there are quality jobs and career paths, there will be incentives for highly trained individuals to “jump” sideways into areas where there is greater demand. Nowadays geodesists come through either the PhD training pathway (from many disciplines), or by receiving “on-the-job” training in geodetic institutes, government agencies, etc. What we need is a large pool of well-qualified scientists (in the geosciences, physical sciences and mathematical sciences) and engineers (geospatial, EE, IT, mechanical, civil engineering disciplines) to draw on. Exciting careers in geodesy, and in PNT technologies and applications in general, will be irresistible.

You had a long association with academia. Given the pace of technology evolution, would challenges you see before the academic community and GNSS education?

Academia educates professionals (such as engineers), and trains researchers (through PhD programs). The former obviously must educate graduates so that they are “jobready”. Some engineering disciplines will therefore use today’s GNSS technologies. They will also be able to adapt to developments in GNSS/RNSS/SBAS. The postgraduates with PhDs will push the knowledge envelope, and hence will bring forth new ideas, new algorithms, etc, for GNSS technologies and applications. When these graduates are employed by companies, they will assist in the development of new products and services. When employed by government agencies they will assist in the implementation and operation of new or upgraded PNT systems (based on GNSS and APNT) for a whole range of applications.

Academics play very little role in promoting GNSS to the wider community. Nor in launching startup companies that drive PNT innovation.

How do you perceive the direction of satellite navigation?

Multi-GNSS is making GNSS PNT commonplace. It is already a capability built into every smartphone. But I believe that there will be a “democratisation” of high accuracy (defi ned as being in the range of sub-metre down to centimetre), so that it will be available on many more devices (including smartphones) to non-expert users. This has challenges for the “experts” in academia (education and research) as well as the geodesy/ geospatial professionals (implementing and operating the infrastructure to support high accuracy positioning).

I believe that the only area of expansion of satellite constellations and signals is for SBAS type systems (as mentioned earlier). These low-cost satellites could deliver augmented accuracy and integrity services by acting primarily as wide-area communications links, transmitting the correction/warning information necessary to enable augmented services.

But I see the parallel development of alternative PNT technologies, being driven by mass market applications such as machine/vehicle automation. In some respects they would be complementary (able to operate when GNSS capability is unavailable), and even seen as backups to GNSS, but some of them, in some scenarios, will be true alternatives (i.e. even competitors) to GNSS. I predict in 1-2 decades that vision systems, INS and alternative ranging systems (both terrestrial and those based on low-cost space transmitters) will have similar performance characteristics to GNSS.

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