Zeus WPI | Building a local positioning system to track runners using Ultra-Wideband Building a local positioning system to track runners using Ultra-Wideband<br>door Robin Paret<br>Geschreven op 2026-07-07<br>Leestijd: 17 minuten

Klik hier om in het nederlands te lezen<br>English<br>12Urenloop is an annual running race at the Sint-Pieters square in Ghent. Participating student association teams run a relay race for 12 hours, trying to complete as many laps as possible. Each team is assigned one baton, so they can only have one runner on the track at a time.<br>Zeus WPI has been doing the lap counting at the 12Urenloop for a while: first through a manual counting system where runners’ bib numbers were entered by hand, then from 2011 onwards with an automatic counting system based on bluetooth modules in the batons. For more background on the historical hardware and software, you can read the 2011 blog post.<br>Between 2019 and 2022 the entire stack was overhauled, with more modern hardware, an estimated position of runners shown on the website, and extensive redundancy, fault tolerance and monitoring. There’s also a detailed blog post about that.

The live tracking site on 12urenloop.be, showing the associations’ team logos estimated positions moving on the track<br>What is UWB?<br>Around the end of October this year I saw some online demos of UltraWideBand hardware using easily obtainable and relatively cheap hardware. UltraWideBand is a radio communication standard focused on centimeter-level localization of transmitters/receivers. This is possible partly because it uses a large chunk of the radio spectrum (500 MHz), which makes it very good at ignoring signal reflections. That means it can identify the very start of a received packet. If you pair that with a clock accurate to the picosecond level, and compare the time a packet was sent with the time it was received, you can calculate how long that packet was in the air (at the speed of light) between transmitter and receiver. Multiply that time by the speed of light and you get the distance between transmitter and receiver. If you can measure that distance to a moving UWB transmitter (tag) from multiple UWB transmitters at fixed positions, you can calculate the tag’s position. This is the same principle GPS uses, just on a smaller scale.<br>This technology is used in, among other things, iPhones and AirTags, to show the distance and direction to an AirTag. It’s also used in newer car keys that unlock the car when you get close, because a UWB signal can be encrypted and is therefore resistant to relay attacks.<br>What does this tech make possible?<br>There had already been talk since 2021 about using UWB at the 12Urenloop, because it offers some major advantages:<br>Exact position measurement: the current bluetooth system gives a good estimate of progress on the circuit (by calculating speed), but no actual position measurements.

With positioning, a lap can be counted at the exact moment someone crosses the start line. This isn’t possible with existing RFID systems used for running races, because at the 12Urenloop there’s a start line per team (at each association’s tent).

More statistics about individual runners: maximum/minimum speed, cornering speed, etc.

A cleaner signal, since there’s a lot of noise from bluetooth signals coming from the hundreds/thousands of spectators.

What you build yourself is usually cheaper<br>Ready-made RTLS (real-time location system) solutions exist, with all the hardware and software you need, but these are outside the budget of a race organized by students (a starter kit from the Ghent-based Pozyx already costs around 5000 euros).<br>In recent years the price of UWB modules has dropped sharply, to around 19-25 euros per module for officially packaged Qorvo modules (used by Pozyx and interoperable with Apple’s U1 chip), and even as low as 12 euros for aftermarket packaged modules (clones) with an integrated microcontroller.<br>So it seemed like a good time to explore how feasible and useful a UWB system could be at the 12Urenloop.<br>On closer inspection, there’s practically no open-source software that supports positioning multiple tags, at least for microcontrollers outside the handful Qorvo supports. Almost all available code focuses on tracking a single tag with multiple anchors, since that’s also a lot simpler. When there are multiple tags and anchors, all UWB modules need to coordinate when they’re allowed to transmit; all communication happens over a single channel, so nothing can talk over anything else. Synchronization between modules needs to be within a few milliseconds to achieve a measurement rate of 1-10 times per second per tag.<br>With that in mind, we ordered 5 DWM3000 UWB modules so we could build a setup with 3 anchors at fixed positions, and 2 tags whose position we determine.<br>To drive the UWB modules we chose the ESP32-WROOM, because they’re cheap (4 euros), have bluetooth and wifi, and were already available in our basement clubroom. The code was...