His Coordinates

“A world of multi-GNSS brings faster and more innovations“

Oct 2023 | No Comment

Says Sherman Lo, President of the Institute of Navigation (ION). He shares his views on a range of issues in an interview with Coordinates

Sherman Lo

Senior research engineer at the Stanford GPS Laboratory. He also is executive director of the Stanford Center for Position Navigation and Time (SCPNT) and a Stanford instructor. His research work focuses on navigation safety, security and robustness. At Stanford, he was Associate Investigator for the FAA evaluation of enhanced Loran and alternative position navigation and timing (APNT) systems for aviation. He currently leads work examining GNSS resiliency, interference and spoofing detection and mitigation. He has over 150 conference, 28 journal, 14 magazine publications and 9 issued US patents. He is the current president of the Institute of Navigation (ION)

Would you like to elaborate on some of the achievements of the ION and also the challenges before?

I feel that ION has done a lot to elevate and bring attention to navigation and its associated technologies and challenges. It has offered a great forum to communicate and publish consistent high quality work in our field.

One tremendous achievement that the ION has made is to bring together a diverse, worldwide group and form a community around that. I have made so many great colleagues and friends from around the US and the world through the ION.

The challenge facing ION is to be able to staying on top of and then fostering new important trends and developments in PNT. Another challenge is in attracting and connecting young people to the community

Can you briefly touch upon your research priorities of Stanford Centre for Position, Navigation and Time (SCPNT)?

SCPNT is about bring together different groups from around campus and industry to work together on challenges that may cross several disciplines.

One example is to develop PNT for ocean science and protecting marine life. The challenges of operating in the ocean and on marine life is different than that encountered in other domains such as land or aviation.

In the oceans, we may not have the luxury of other communications channels, good satellite visibility or even much more than a few seconds to receive satellite signals. So we are working to develop fast offline positioning that can provide position in a few seconds without the need for external networks. In this effort, we work with the School of Humanities and Science (Department of Biology).

Another SCPNT research area examines concepts for the next generation of satellite PNT, whether that be augmented constellations, low earth orbiting satellites or secure navigation signals.

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

The most evident benefit of multi-GNSS is that it bring more satellites, more availability and more choice leading to better performance. Another, less obvious benefit, is that a world of multi-GNSS brings faster and more innovations due to the competition between the different systems. So now there are systems offering high accuracy, navigation message authentication, improved signal design, and service improvements. Currently every system seeks to measure themselves against GPS which pushes them to improve performance and offer new features. In turn, this pushes GPS to incorporate new features and provide greater functionality.

Would you like to comment on GPS III and also on other existing and upcoming systems?

Not much to say except it is exciting to see these improvements to current systems as well as the upcoming systems come online. The GPS IIIA and IIIF bring new technologies and capabilities. Future satellites such as the next generation Galileo will have more flexible transmission capabilities. The Koreans are developing the Korean Positioning System (KPS) and Africa is working on their Satellite Based Augmentation System (SBAS) system. I am also excited to see the development of low earth orbiting (LEO) navigation constellations, both governmental or commercial. Not only does having LEOs bring geometry benefits, LEO satellites can be more quickly and cost effectively refreshed allowing new capabilities faster.

With increasing dependence on GNSS, how do you the perceive the threats like interference, jamming and spoofing?

Interference is an important problem. Even relative straightforward jamming events (and even jamming exercises) has cause some disruptions to GNSS dependent operations. We’ve seen several interference events have some effect on air traffic – most prominent of which is in the eastern Mediterranean. The challenge is that the threat we have to deal with is evolving. There is greater ease of access to the means to implement those threats. Attacks that were hard or very expensive a decade ago are within the means of determined individuals today. The Ukraine war again showed the importance of GNSS and that denial and deception of GNSS will be used as tools. So we need to deal with this reality. On the technical side, Prof. Brad Parkinson talks about protecting, toughening and augmenting (PTA) GNSS. I agree with this concept. We need to have laws, policies, and infrastructure in place to protect GNSS. We need to develop AND implement technologies on GNSS to toughen its use, Finally we should have means of navigation that are independent of GNSS. I believe we have many of the ideas, methods and technologies (antenna technologies such as CRPA and polarization antenna, internal receiver metrics like AGC & C/No, or examining the complex ambiguity function, etc.) to really make GNSS robust against most interference threats. They may still need to mature more but they exist, are implementable and, I believe, can be cost effective. The challenge is getting all parties (decision makers, manufacturers and customers) to recognize the need to have these in place.

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

I worked on non-GNSS navigation systems for much of my career and it is near and dear to me. So naturally I think “back ups” are absolutely necessary – especially in critical applications. However, I don’t like to think of them as back ups but rather a part of a navigation ecosystem or strategy. The community is working on hardening and improving GNSS to attacks as discussed earlier but it is may not be enough for the most determined adversaries. So I think GNSS “back ups” are absolutely vital – a prudent navigator should have multiple independent means. We should be thinking of navigation not as a single system but an ecosystem of systems which includes non GNSS means. There is a reason why we still keep traditional terrestrial navigation aids in aviation. I think the important aspect of the alternates is that we need to develop them so they provide capabilities similar to GNSS, and preferably, features that either compliment GNSS or that are not found in GNSS. This provides incentive for adoption as well as deterrence to people who want to harm GNSS and navigation.

What technology trends you envision in GNSS and what kind of innovative applications you anticipate in near future?

Application of artificial intelligence (AI) to different fields is the current hot topic and it certainly is the case with applications of it to GNSS. Related is autonomy (which has employed a lot of machine learning and AI) and navigation to support autonomy (see later answer). In the last year, we’ve seen a significant uptick in research and publications on lunar and cis-lunar navigation along with a further growing interest in LEO PNT. I suspect as access to space further improves and we think about landing more sophisticated or even human missions to Mars, we will need the precise navigation infrastructure there to support that.

Getting back down to earth, I see at least two trends. First, integration of even more navigation sensors (inertials, barometer, 5G, WiFi, GNSS, etc.) will improve performance and availability of accurate positioning. The trend towards greater connectivity between our vehicles may lead to more coordinated or distributed positioning where we integrate measurements from multiple distributed users (vehicles). Second, is improved processing. We have more satellites, more data, and more user processing capabilities and so we can potentially squeeze more performance out of GNSS. Improved processing can come in many forms. In the past decade, PPP really came to the forefront in the last decade. More recently, we have seen things such as the use of factor graph optimization to improve position solutions and the development and incorporation of super correlation into consumer devices. These three are operate in different parts of the GNSS PNT processing chain – PPP is infrastructure, super correlation is receiver processing while factor graph is post receiver processing. It just goes to show that there is still innovation and possibilities in many aspects of GNSS.

How do you think the GNSS positioning technology can take the advantages of alternative positioning technologies cell phones, Bluetooth and WiFi, etc?

I am not saying any novel or new but 5G promises more dedicated positioning capabilities with better capabilities than prior generations. We can get potentially a lot more indoor navigation signal. That and more GPU power in consumer devices allow us to accurately model both direct and in direct signals to get accurate positioning. More specifically, this benefit to GNSS is in providing combined hybrid solutions which is particularly for needed urban and indoor navigation. With these data channels we can use them for improved performance (e.g, PPP corrections) or security (e.g. authentication capabilities).

How do you see the impact of Generative AI in positioning and navigation domain?

I don’t have a lot of expertise in that but I’ll comment on machine learning (ML). A lot of GNSS research at the university level has applied ML techniques. Through large amounts of GNSS data, it may be able to provide improvements in accuracy. That is where ML is powerful – it may be able to find relationships in the data that we may not readily identify, allowing to be leveraged for greater performance. However, working in the safety of life field also makes me cautious about its use in certain applications as sometimes it may find relationships that are not really there.

Would you like to comment on autonomous navigation?

That is a very broad question. Autonomy and autonomous navigation means different things in different eras. Today we imagine autonomous cars and how they will be able to negotiate typical human driving (A side note – they are not quite there yet – I just saw one make a stop in the middle of the street with no cars ahead of it). In past eras, it may have been a space probe or rover that has to operate without much intervention. The scope and domains of course is increasing as we get ubiquity and redundancy in navigation, it will filter into more and more categories. In the early days, it was very specialized tasks but now autonomy in more challenging or everyday tasks. But only because we have the navigation to support it. It is a feedback loop. What we provide in PNT helps drive what people think is possible with autonomy which then challenges us to create PNT systems that can achieve that dream. For example, in the original DARPA grand challenge participants relied a lot on GPS. Of course, it wasn’t robust enough which drove innovations to supplement GPS with other sensors, AI, etc. to get a vehicle that could complete the challenge.

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

I group challenges in GNSS in three categories based on the audience. I have many undergraduate students who are curious about navigation because of their phones and google maps. For them I think the challenge to get to generally understand which role navigation and timing technologies play in their lives and generally how these technologies work. For some it is a little like magic which is dangerous. I want them to gain basic understanding and limitations of these common navigation tools so they can use it safely. I don’t want to still be reading about people blindly depending on their satnav devices leading them to danger.

For students in the field, I think the allure of the next shiny hot topic needs to be tempered with fundamental understanding. Of course ML and AI are the current hot things and they have great utility. But some things still require basic physics and math. AI while not magic is somewhat of a black box. And as we use our navigation system for critical applications, the safety of their results can’t be a black box (or at least you have to have some well defined means of checking that box). So use ML but also learn, understand and use the fundamentals to complement those techniques.

For the academic community as a whole the challenge is getting people into the field. We recently had a meeting at ION GNSS 2023+ discussing this very issue. It is a complicated problem as it involves getting young people into STEM as well as letting them see that there is such a thing as a career in PNT. I certainly didn’t know that this was a field when I was an undergraduate. I was fortunate to stumble into GPS while doing some flight test work in the early 90s. We can see from industry and government that there is a demand for people with PNT skills. The challenging task is attracting and training capable people into PNT. It is a great field to be in, with great people and I am certainly lucky to be working in it.

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