# Welcome!
# Audio propagation analogy I like to introduce my subject with a small analogy.
Let the speaker emit audio waves towards the audience.
Let us focus on one of the listeners.
In free space, sound arrives in a direct path.
But what if we have a wall?
Like in a tunnel, the sound waves will reflect on this wall, and reach the listener a second time, with a different delay and volume.
Of course, we can have many walls.
Or obstacles that obstruct some paths.
What if the target changes?
Of course, the same logic can be applied to radio networks.
What we did, if actually called Ray Tracing (RT)
Table of contents
RT and EM Fundamentals
We are interested in broadcasting waves from a BS
In a simplified model, the BS emits waves isotropically.
Using Huygen's principle, we can decompose a wave front into a series of new wave sources.
Each source now broadcasts waves, each with a fraction of the original energy
RT considers each ray path individually.
In a constant speed space, ray paths are linear.
Maybe, we reach some obstacle.
If we decide to apply reflection.
We can do that for very complex scenes and many paths.
Example of tracing paths in 3D Urban scene.