Benoit Debled

Software Developer
Firmware Developer

Master Thesis: Distance measurements using LoRa

Nowadays, we use geolocation more than never: in our smartphones, in our cars,... One of the most used system is GPS (Global Positioning System) as it provides good accuracy. Even though we use geolocation a lot right now, we will use it even more in the future, hence the need to diversify and improve geolocation systems.

Conceiving a distance measurements solution and conceiving a geolocation solution is very similar as to conceive a geolocation solution, one needs to measure the distances between three anchors and a mobile. As the anchors positions are known, it is possible to find the mobile position.

This master thesis has for purpose the conception of a solution to measure distances between two nodes with precisions by using the GPS time and LoRa transceivers. This technique has the potential to be more accurate and have an higher refresh rate than GPS.

Using the Time of Arrival (ToA1) technique, we calculate the time that takes a message to go from node A to B using LoRa transceivers. Knowing that a message travels at the speed of light and the amount of time it took for a message to travel, we can infer the distances between the two nodes.

As ToA requires clock synchronization, a GPSDO is used on both nodes. All GPS receiver offer a pin called 1PPS (1 Pulse Per Second) which as its name indicates give one pulse per second. Those pulses are very accurate. A GPSDO is simply an oscillator that is disciplined by a 1PPS signal as its name indicates: GPS Disciplined Oscillator.

1 ToA: The Time of Arrival technique is used to determine the propagation time between two transceivers A and B. Both transceivers need to have their clocks synchronized. To know the propagation time between A and B, A sends a message containing the current time to B. B saving the time of received messages can therefore figure out the propagation time by subtracting the received time by the sent time available in the message content.