Identifying modulations – a didactic example

What we now have is a very common question when looking into unknown signals: what is the modulation? Finding the correct modulation and parameters can require a bit of detective work, even if you know the parameters. This section is more of an illustration of the process of reversing a signal modulation than directly a recipe (since there is no recipe). Some people are currently working in an academic context on projects to train neural networks to do signal classification, meaning there is no straightforward way to recognize modulations.

In the case of the light controller, we can already reduce the candidate's number because we know (from the FCC documentation and opening the device) that it embeds a CC2500. The datasheet tells us that it supports a few modulation schemes: 2-FSK, GFSK, MSK, and OOK. We already eliminated two (OOK and FSK) but how do we tell the difference between them?

First, let's talk about what...