Fixing interference in GPS

Multi-path interference makes GPS less accurate. How might you fix it?
22 December 2020

Interview with 

Ramsey Faragher, Focal Point Positioning


Earth from space


Possibly the most important traveller around now is Santa Claus, and to make sure he gets to all those houses on time he needs a really good GPS. Imagine if the GPS told him he was at a nice child’s house, but was actually at they’re naughty neighbour. Well a Cambridge based company, Focal Point Positioning, has teamed up with a European company, u-blox, to help fix a key weakness in the technology, multipath interference. Adam Murphy heard how it works from Focal Point Positioning CEO, Ramsey Faragher...

Ramsey - It's the effect that's caused by lots of echoes of a radio signal, bouncing around inside a city, confusing your GPS chip and making it calculate a wrong position. It's a bit like trying to host a very loud dinner party inside a big cave. It would quickly turn into a noisy confusing cacophony, due to all of those echoes. And GPS is designed for open spaces where there are no signal reflections. This problem of multi-path interference, the problem of signal echoes from buildings has actually been the biggest cause of bad GPS fixes for the last 20 years.

Adam - Now, given all that being true, my phone's GPS is still pretty good. So why is fixing this and making it better, so important?

Ramsey - So it's true that on a good day out in the open, that little smartphone in your pocket can work out where you are to within a few metres. And that is then both a blessing and a curse, because if you become very reliant on that good accuracy outdoors in the middle of nowhere, when you go and try and use that GPS in the middle of downtown New York, or London city centre, or Tokyo surrounded by big, tall reflective buildings, and only then do you discover that it's actually quite inaccurate in those places. It can cause you major problems, your taxi turning up on the wrong side of the street, your food delivery going to the wrong house. In future problems for drone deliveries, getting it all wrong. Autonomous cars, not being able to navigate safely in amongst the tallest nastiest buildings. And that's what we fixed. And it opens up lots of new opportunities for metre level positioning right down there amongst the skyscrapers.

Adam - Well then I suppose the key question to ask you is how does it work? What is your solution?

Ramsey - We went right back to the very lowest level of the physics of the problem, and created the fix right from there. So when the signals bounce around, that means they're coming at you from the wrong directions now, relative to the actual location of the satellites in the sky. And we do always know exactly where those satellites are, but the GPS chip itself has never been able to work that out. It can't calculate the angles that the different signals are coming from. The only way to do that normally has been with a very, very expensive antenna. I'm talking about thousands of pounds for an antenna. It'll never be on a smartphone, but what we figured out, was a way to change the software inside the GPS chip itself so that it can now calculate all of these different angles of arrival, of all of the different signals and unpick them from each other, and separate out the one line of sight signal you want from all of the echoes you don't want. And we can make the chip ignore all of those echoes and voila, no more multipath interference.

Adam - So it's like when you got a tangled mess of headphones in your pocket, the phone is now doing software to unpick that, to get your headphones back to what they should be.

Ramsey - Yeah, exactly.

Adam - And is this something that can be easily implemented everywhere, in every phone, or are there some really key focused applications?

Ramsey - So it is just a matter of upgrading the software inside the GPS chip. And that then means we can solve multipath for any device that uses radio signals to navigate just like GPS. So any application for a moving GPS receiver, we can help, but my company itself cannot change the software on the GPS chip completely on our own. The change has to be made by the manufacturer, that software change only takes a few months to do. In reality, getting a billion-dollar GPS chip set company to hand over the keys to their pride and joy, to my startup, doesn't happen overnight. And so we generally have to do quite a lot of trialing and verification with those companies to prove that our tech does what we say it can, but we've made great progress with major GPS chip set companies. u-blox being the first deal that we can publicly announce, and there'll be many more like it in the future. And I can also announce here on the Naked Scientists for the very first time, that Focal Point Positioning has also been working very closely with Santa for many, many years now. And we always help to ensure that he never has any navigational problems on his big night out.

Adam - It's very important to know Santa will be safe, what's next then, what's the future of this kind of technology?

Ramsey - Well, the exciting thing is that we can help bring one metre positioning to your smartphone in cities right now, with the current generation of GPS chips. But next on our roadmap is trying to get that right down to 10 centimetres. Maybe even down to two centimetres, that's the sort of thing we're aiming for in the future. And then that will open up a whole host of new ways that people can make use of GPS for all sorts of exciting new purposes.


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