I am currently taking part in a project in which I am building drones using Arduinos and Raspberry Pis, and I need to be able to measure the distance between the drones. After some research, I realized that many people use ultrasonic sensors.
However, I want to build a system that can measure the distance through walls and over moderate distances (up to 100 meters.) I figured that ultrasonic sensors won't have this range, and might not work through walls. I am honestly stumped with how to solve this problem.
Is there a way to do this, or is that just not a practical idea?
I want to have an accuracy of at least within half a meter.