The satellite-free alternative to GPS

Host: Nick Petrić Howe

Welcome back to the Nature Podcast. This week: a global positioning system that doesn’t need satellites.

Host: Shamini Bundell

And updates from the Nature Briefing. I’m Shamini Bundell.

Host: Nick Petrić Howe

And I’m Nick Petrić Howe.

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Interviewer: Nick Petrić Howe

If you’re like me, you’ve probably become quite reliant on the little blue dot on your phone which tells you your location. It’s useful for finding your way and also letting people know where you are. For it to work, it relies on at least four satellites being able to directly ping your phone. The signals from each satellite are then interpreted by your phone to tell you your location. But the thing about satellites is that they are in space, and space is very far away.

Interviewee: Christian Tiberius

So, the signal, the radio signal, has to travel a lot, a long way. And therefore, when it arrives here on Earth, it’s very weak.

Interviewer: Nick Petrić Howe

This is Christian Tiberius, an expert on navigation using radio signals. Because this signal is so weak by the time it gets to Earth, it can be very easily disrupted. You have probably seen this yourself, when you’re looking at the little blue dot and it wanders away from where you are.

Interviewee: Christian Tiberius

Yeah, exactly, and that's by blockage of the radio signals by buildings in urban areas. And to make it even worse, these buildings also reflect the radio signals so that you still receive the signals but actually with a significant detour, that's then confusing your GPS receiver. That's why it starts to wander around in urban areas and deviating from the actual track.

Interviewer: Nick Petrić Howe

This certainly explains why my blue dot tends to wander all over the place in London, meaning that sometimes my deliveries end up a street away from me because the driver doesn’t know exactly where they are. But anyway, back to the story. Now, scientists have been long aware of these problems, and so many systems also use mobile phone networks, with the satellite signal being augmented by mobile phone masts that do a similar sort of pinging as the satellites do. But this lacks accuracy, as mobile phone masts are not very synchronised in terms of time. And when it comes to finding your location, timing is of the essence. To determine your location, satellites all send signals at the same time, and the amount of time these signals take to reach you from each satellite tells you where you are. If you’re closer to one, then it’ll take less time for a signal to reach you than one far away, and this difference tells you your position. But when you’re dealing with speed-of-light radio signals, tiny errors make a big difference. Here’s Jeroen Koelemeij, an expert in precise measurement, to explain.

Interviewee: Jeroen Koelemeij

If you realise that the speed of light is almost 300,000 kilometres per second, which means that if your transmitter has a clock error of 1 nanosecond, the error will be 30 centimetres.

Interviewer: Nick Petrić Howe

This is why satellites for navigation have highly accurate atomic clocks in them. But even then, we still see all of these errors, especially in urban areas. So, Joeren and Christian have been working together on a solution for many years, which doesn’t need satellites at all. Here’s Jeroen.

Interviewee: Jeroen Koelemeij

Well, the solution is actually to replace the satellites and the atomic clocks in the satellites by an infrastructure that could be based on the existing fibre-optic network, that you connect to a single atomic clock, and you distribute the time signals of that clock through the fibre-optic network. The next step that you then take is you connect the, let's say, antennas of the mobile network, you connect those to the fibre-optic network, and they are synchronized to this atomic clock. And then they can play exactly the same role as a GPS satellite does, but on Earth.

Interviewer: Nick Petrić Howe

Rather than rely on multiple satellites and clocks, whose signals can be disrupted, in their system, the optical network is able to quickly distribute timings from a central atomic clock to the antennas. These antennas are accurately synchronised using a specially developed algorithm, and they transmit radio signals that are picked up by the receiver that figures out the position. So, how well does it work? Well, by transforming a part of Christian's campus, the team put it through its paces. Here’s Christian.

Interviewee: Christian Tiberius

We built the prototype, actually consisting of six transmitters, and we deployed it here at an experimental site at the Delft University of Technology campus. So, it's really outdoors. It's not in the lab. And there, we took several tests, principally with a trolley and also with a car, at low speed, obviously, at the campus, but really demonstrating that the system not only works in theory or on paper but also really in practice.

Interviewer: Nick Petrić Howe

And as the team were pushing their trolley or slowly driving around the campus, they saw that the system was able to accurately place them to within 10 centimetres of where they actually were, which appears to be better than how conventional systems fare in the same sort of built-up environment.

Interviewee: Christian Tiberius

Let's say a standard GPS receiver in the same environment and same setup. It's a built-up environment so there are reflections from buildings around. We will typically see performance at the several-metre level from GPS.

Interviewer: Nick Petrić Howe

The team were also able to use higher bandwidth signals compared to conventional satellite systems, which are also less affected by things like buildings being in the way, as you’re able to send more information which can still help you find your location even when the signal hits objects. According to Jeroen and Christian, implementing their system in the real world would be relatively straightforward as it could utilise existing fibre-optic networks that are used for internet connections. Here’s Jeroen.

Interviewee: Jeroen Koelemeij

From a technical point of view, I think there are no barriers to implementing this in the real-life network and in the equipment. It would just be a matter of doing the investment. But once the paper has been published in Nature, then, yeah, maybe other people will read about it and it might be an eye opener for them, and it might actually accelerate the implementation in real-life networks.

Interviewer: Nick Petrić Howe

And while it may be ‘just a matter of doing the investment’, this could be a significant hurdle for the team.

Interviewee: Dorota Brzezinska

So, to me, scalability of this and the cost, which comes with scalability, is the question, right?

Interviewer: Nick Petrić Howe

This is Dorota Brzezinska, a researcher of satellite navigation systems, who wasn’t involved in the new paper. Whilst she was impressed with the accuracy the team were able to show, she wondered who might be interested in paying for it?

Interviewee: Dorota Brzezinska

I do like the demonstration, how the demonstration was done very carefully, and it's not like a tiny area. So, I think it is scalable. But again, for them to accomplish this accuracy, they need specific density and geometry of transmitters, so not sure what the cost is going to be.

Interviewer: Nick Petrić Howe

And whilst there are obvious barriers to us seeing the technology in place in the near future, the team behind it envision using this primarily in urban areas, where there is a specific need for high-accuracy positioning, and where there are more likely to be disruptions to the signal. And if you can get reliable positioning in cities, the team think it could be useful for all sorts of applications, like drone delivery while you’re on the move, and the development of smart cities, and maybe even in self-driving cars. Here’s Jeroen again.

Interviewee: Jeroen Koelemeij

Our technology could really help there also because it can provide enhanced positioning accuracy at the 10-centimetre level, which is ideal if you want to know which lane you're in, for example, on the highway.

Interviewer: Nick Petrić Howe

In the least, the team believe that this could be an important back-up for when conventional satellite systems go wrong, as the whole world is very reliant on it. But for me, I was just excited that it may be able to solve one of the banes of my existence. I will just be happy once delivery drivers actually come to my house rather than the next street over, which is what they normally seem to do because of GPS.

Interviewee: Jeroen Koelemeij

That kind of problem, that's exactly what a system like ours could solve for you.

Interviewer: Nick Petrić Howe

That was Jeroen Koelemeij from Vrije Universiteit Amsterdam in the Netherlands. You also heard from Christian Tiberius from Delft University of Technology, also in the Netherlands, and Dorota Brzezinska from The Ohio State University in the US. For more on this story, you can find a link to the paper and a News and Views article in the show notes.

Host: Shamini Bundell

Coming up, after weeks of deliberation, COP27 has wrapped, and we'll be hearing about what was decided, including a hotly contested global fund for climate damage. Right now, though, it's time for the Research Highlights with Noah Baker.

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Noah Baker

New research is predicting the extinction of a rare lemur species within 25 years if action isn't taken now. Milne-Edwards’s sifaka, like all lemurs, is only found on the island of Madagascar. And like many of its lemur cousins, it's facing a whole host of threats from climate change to habitat destruction and poaching. And now researchers have used 34 years’ worth of data on the sifaka’s population to try to get a handle on where the greatest threat is coming from. By combining these population data with information on extreme climate events and human activities, they were able to model the chances of a sifaka survival. And it turns out, the number one threat for sifakas is deforestation. The group estimated the species could become extinct in about 23 years if deforestation continues at the rates that have been seen recently. But that isn't the only risk factor. For example, if deforestation is lowered, but tropical cyclones and droughts occur more frequently as a result of climate change, the sifaka population will still decline by about 20% in the next two decades. But they say, in that situation, extinction within the next 50 years is unlikely. The authors are using this research to call for policies that focus more on reducing deforestation and expanding protected areas in Madagascar. Read more in Biological Conservation.

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Noah Baker

Chemists have devised a simple method to make plastics using light, and they hope it could open up new ways to use some of the world's most common plastics like polyethylene and polypropylene. Plastics are made up of chains of molecules called monomers, strung together in a process called polymerisation, usually with a little help from a catalyst. By controlling how these monomer building blocks are joined together, researchers can make plastics with unique structures and properties. And now, they're experimenting with a new way to control the process with light. They start with a gaseous mixture of monomer building blocks, catalysts and special compounds called photoacid generators. Then they expose the gaseous mixture to UV light, shaded to create specific patterns. The light excites the photoacid generators, which causes them to release charged particles, and that in turn activates the catalysts and triggers the polymerisation reaction. They use this method to build thin films of plastic from gaseous ethylene and propylene. The authors hope the technique could be developed to create new 3D-printing processes, which could create plastic structures from gaseous feedstocks. You can read more on that research in the Journal of the American Chemical Society.

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Host: Nick Petrić Howe

Finally on the show, it’s time for the Briefing Chat, where we discuss a couple of bits of news from the world of science. Shamini, what have you been reading this time?

Host: Shamini Bundell

Well, I’ve got an article from the Nature’s careers section, which has come out of a big survey that they’ve done of graduate students around the world. And this particular article is looking at the data from international students.

Host: Nick Petrić Howe

We’ve talked about a few times different careers surveys on the podcast about how graduate students are doing, so what is different, or, I guess, what is specific about how international graduate students are doing?

Host: Shamini Bundell

Well, international students obviously face particular challenges during their studies that domestic students might not – travelling outside of their home countries to study. So, in this particular survey, they've got almost 1,000 international students. And one of the interesting things just sort of straight off the bat from the data is that they had, of the people who answered the survey, 29% of them were international students, and that's actually down quite a lot from the last time they did a survey like this, which was 2019, so obviously pre-pandemic, when it was 37%. So, 29% now, down from 37% international students before, so potentially the pandemic has had quite an impact on that.

Host: Nick Petrić Howe

Oh, I can see how the pandemic would make things difficult. Travelling was quite hard in that time. But does the survey reveal any like reasons why people may not be moving away from their home country?

Host: Shamini Bundell

Well, the surveys are sort of focused on the people who have, and basically asked them, ‘What prompted you to study in a different country?’ And actually, the biggest result from that was to experience another culture, which was like almost half of the international students who responded. But also, a whole bunch of other stuff that was driving quite a lot of people, such as lack of funding opportunities in their home country, more job opportunities after they've completed their studies, in some cases, a lack of quality graduate degree programmes in their home country, or a sort of specific research question that they wanted to study that maybe wasn't available where they were.

Host: Nick Petrić Howe

And when we've talked about other surveys that the careers team have done, we've heard that graduate students are feeling quite stressed. They've got a lot of challenges facing them. What's it like for international students who probably have additional things like visas and stuff to worry about?

Host: Shamini Bundell

Absolutely. Visas is one of the big ones, and they've actually interviewed a PhD student based in Poland, who is an Indian PhD student who was talking about the visa sort of process that he has been having to go through, which is basically he had to keep reapplying for successive one-year visas, and each application took 6-9 months to process. And while it was being processed, he couldn't travel to any international conferences or take any samples to any labs outside of Poland. He says it extended the length of his PhD and described the bureaucratic process as ‘a nightmare’. Although, that doesn't necessarily translate to international students not being happy with their degree programmes. So, the satisfaction with the graduate school experience is actually very slightly higher for international students than it is for domestic students. And this particular PhD student sort of compares the resources available in Europe compared to India, and notes that it's not as pressurised where he is.

Host: Nick Petrić Howe

So, maybe, for them at least, there were more opportunities in other places that may make it worth these sorts of challenges. But considering those challenges, were there any other examples that they found through doing this survey?

Host: Shamini Bundell

So, this is just one sort of article reporting on one part of the survey, so there's going to be a lot more coming on this in the other articles in the career section in Nature. But one interesting thing was the answer to, ‘Have you experienced discrimination or harassment during your programme?’ With international students, more of them said yes – 26% compared to 17% of domestic students – and of those who said yes, over half said that they'd experienced racial discrimination or harassment. And there's sort of an example of that in the article as well from one of the interviews, where a student was talking about one of their professors, who was extremely picky about the students’ language and pronunciation and grammar, apparently driving another colleague to quit just because of this sort of constant, what was described as ‘over the top’ criticism.

Host: Nick Petrić Howe

Oh, well, crikey. Well, hopefully, this article and the series of articles that are coming out of careers will help shine a light on some of these problems, and potentially help with tackling them in some small way. For my story this week, we've been talking a lot about COP27 recently on the podcast, and it is now finished. So, I wanted to spend a little bit of time talking about what was decided at the end there. And I was reading about this in multiple places, but the bulk of what I'm going to talk about was reported in the New York Times.

Host: Shamini Bundell

So, we had Flora on last week who was actually at COP27, sort of talking about what was going on in the midst of it. What's the big news that’s sort of come out of it now that it's finally concluded?

Host: Nick Petrić Howe

Well, the big headline thing is that there is now going to be a fund to address loss and damage. So, this is the concept that many countries are going to suffer the brunt of the effects of climate change, but they've actually not contributed to climate change very much. They're often lower-income countries, and most of the past emissions have been by higher-income countries. So, the headline is that now these higher-income countries that have caused many of these emissions will make a fund that will be available for these lower-income countries that are going to suffer most of the damages to access.

Host: Shamini Bundell

And are a lot of high-income countries actually going to put money into this fund?

Host: Nick Petrić Howe

Well, that is the big question. About a decade ago, a group of higher-income countries came together to agree to put US$100 billion every year in climate finance to be available for lower-income countries. But thus far, they're still falling short of that by tens of billions of dollars every year. So, there is a big question about whether anyone will deposit money in this fund. And obviously, as well, the situation has changed slightly in the US recently. You may have seen that there was a midterm election and that meant the House is now in Republican control, as of January, and even when the Democrats controlled both the House and the Senate, they still struggled to put as much money towards climate action as President Biden wanted. So, it will be an even bigger challenge with a Republican-controlled House. So, there are real big questions about whether this money will actually get there, but for some countries it’s a key step forward because this has been a hotly contested thing for a long time because many wealthy countries, in particular the US, have been opposed to it because they were worried about writing what they see as a blank check.

Host: Shamini Bundell

So, it seems like we’ve finally taken a step that lots of people were waiting for. Are people happy? Are people optimistic about this?

Host: Nick Petrić Howe

There is optimism because of this. So, the climate minister of Pakistan said that the announcement offers hope to vulnerable communities all over the world who are fighting for their survival from climate stress. And as I say, this is something that many countries have been pushing for, for a long time. So, it is quite a momentous thing. However, there is a cloud hung over it because, whilst this has been announced, there has been less movement on dealing with the root causes of climate change – the emissions that are going on. So, last year at COP26, there was a push to really try and reduce emissions. But the pledges haven't really changed from last year. And a recent UN report said that the current pledges will put us on track to 2.4 °C to 2.6 °C of warming, which still would lead to many dramatic impacts and the loss of like low-lying island nations and that sort of thing. And that's the current pledges. With current policies that are actually in place, we're actually looking at more like 2.8 °C. And for many people, it's really, we need more action, like these sorts of pledges are very good and this fund is great, but is it just sort of a fund for the end of the world? We actually need to make a bit more movement on the emissions side of things.

Host: Shamini Bundell

Is there anything else sort of particularly novel that's come out of this particular COP that it's achieved?

Host: Nick Petrić Howe

The other big thing that's come out of this is the United States and the European Union secured language in the deal that could expand the number of people who contribute to this fund. So, historically, places that are considered developing by the United Nations, like China, were excluded from providing aid. But actually, now, they may be included in this. But of course, this will be a hotly contested thing as well going forward.

Host: Shamini Bundell

So, COP, overall, from what you've read, do people feel that it was a useful conference?

Host: Nick Petrić Howe

As with most of these, it really depends on who you ask. For some, I'm sure they'll be very happy with this, to make these small, incremental steps. But I think, actually, for the large majority, it's really, we need to do more and we do need to do it more quickly. So, to keep warming to 1.5 °C, which is the target from the Paris agreements, that would require emissions to be reduced by 45% by 2030, and that is very rapidly approaching. And with things like the war in Ukraine and the sort of global financial situation at the moment, it's looking more and more tenuous that this will actually happen, and policies need to be put in place, more needs to be done to tackle climate change. But this is the same thing that we always say when we talk about these sorts of stories.

Host: Shamini Bundell

Well, climate change is not going away, so neither will our reporting of it, I'm sure, so keep your ears tuned for more on this topic. And if you want any more details on the stories that we've discussed, and to find out where you can sign up for the Nature Briefing so you can get more stories like this in your email inbox, you can check out the show notes for some links.

Host: Nick Petrić Howe

That's all for this week. But before we go, Shamini, I believe you've been making a video and it's all about sand. Do you want to tell our listeners a little bit more?

Host: Shamini Bundell

It is! It’s about a sandcastle. No, it's actually about a very important topic, once again, linked to climate change. It's this whole concept of the circular economy. And in order to illustrate this topic, I hired some sand sculptors who made this amazing sort of sandcastle art piece out of an enormous pile of building sand. So, check out the show notes for a link to that YouTube documentary.

Host: Nick Petrić Howe

It is well worth watching just to see the massive sandcastle sand art installation, never mind all the cool science. But that's all we've got time for. So, if you want to keep in touch with us, you can. We're on Twitter and we’re @NaturePodcast there. Or you can send an email to podcast@nature.com. I’m Nick Petrić Howe.

Host: Shamini Bundell

And I’m Shamini Bundell. Thanks for listening.