Solving the problem of indoor localization

Technical Pride: Solving the problem of indoor localization  


In this article, we dive into the achievements of our researchers. This time, we tackle the topic of ultra-wideband pulse and ultra-wideband pulse-based ranging; a topic for which Chris Marshall, member of the technical staff at imec the Netherlands, received an award during imec’s Intellectual Property Day 2023. 


Time of Arrival (ToA)  

From keyless entry solutions for vehicles to asset tracking in warehouses or factories: measuring the location of devices is becoming increasingly important in modern life. We use GPS every day, and it’s marvellous, but the satellite signals are too weak for it to work indoors. For indoor and Internet of Things applications we use the emerging wireless technologies of Bluetooth and Ultra-Wide Band (UWB) short range radio. But it is still a challenge to measure the so-called Time of Arrival (ToA) very accurately. “That is the heart of what we are doing”, Chris says.


“We find that the leading edge of a transmitted pulse shape plays a particularly important role in the estimation of the ToA of the pulse by a receiver. For example, in the case of secure access to your car there is not only the direct signal which goes from your tag to the car: it also bounces off the ground, ceiling or walls. Not only do you need to measure the direct path ToA, but it is also crucial to prevent confusion caused by these other, reflected and scattered multipath signals.”  


“To do so, we want to sharpen the first pulse – making its leading edge as sharp as possible, because the sharper that is, the more precisely we can measure it. Our application improves the precision with which we can measure the pulse’s ToA, which in turn will improve the accuracy with which applications can measure the range between devices.”


All good fun

Chris loves to discover new things. “Development for me is continuously moving forward. Stretching the existing into something new. I believe uncertainty is a good thing, it creates opportunity. Uncertainty is often thought to be a problem because it has risks associated with it. The trick in development is creating new opportunities while managing the risks. I believe you need to embrace uncertainties, otherwise we would never move forward, which none of us wants, particularly here at imec.”


Creating things for humanity that we can do now, which we couldn’t do before is what drives Chris. He brings in a lot of experience and knowledge as he was involved in the very early stages of turning radios into integrated circuits, the start of digital radio in its forms nowadays, like paging receivers and GSM cellular phones. He joined Philips in 1980 after graduating from Cambridge University (Natural and Electrical Sciences). While working at Philips, he also obtained a PhD at Imperial College, London.  


“I was with Philips Research, and we did all sorts of wonderful things. It all started with developing pocket pagers for doctors, based on new (direct conversion) radio concepts that could be integrated onto a single chip, including the channel filtering, with minimum external components. All good fun!” Chris also worked for NXP, its spin-out Geotate, and the Swiss company u-blox. In 2021, he got the opportunity to move once more to continental Europe, coming to Eindhoven to work at imec at Holst Centre.




“At imec I try to bring together the different aspects of what you can do with all this technology. How can we feed new features into the circuits and software, allowing us to make exciting new things? How can we sense wireless signals, and find good solutions to the unsolved, difficult but invaluable problem of indoor positioning? I like to juggle concepts to fit them together. It is a bit like learning a new language. You are reading this strange stream of words which don’t make sense. It is a matter of juggling the meanings - and using the context - of the words to understand what is happening. I enjoy it.” 


Nevertheless, Chris readily admits that his wife speaks better Dutch than he does. “She is a member of two instrumental groups, she plays the clarinet, and she is the secretary at an English Bowls Club here in Eindhoven (English bowls, a sport also known as lawn bowls or lawn bowling, red.). I’m in the process of joining the local chess club”, he adds with a playful wink.


Besides Chris, the inventors in this patent application were Erwin Allebes, Elbert Bechtum and Minyoung Song. 


The generation of such a pulse shape involves some innovative circuitry and is described in a paper on imec’s latest UWB transceiver by Minyoung Song and the team, presented at the 2023 VLSI conference. A paper on the pulse shape itself has been written by Erwin Allebes, Alireza Sheikh, Minyoung Song, Mohieddine El Soussi, Nick Winkel, and Chris Marshall, and has been presented at the Indoor Positioning and Indoor Navigation conference in September 2023.