How to transmit and receive custom wireless data using Android's inbuilt baseband SoC?

I want to transmit and receive custom wireless data by using Android's baseband. So the question remains: - How to do it? - Is that true that the baseband operates on separate SoC & separate firmware? - If the baseband operates on different firmware, then can it be changed? - As we know, OTA updates exist on Android, so it means it's possible to upload a different firmware. But, is it possible to change the baseband firmware using a Cable-USB-PC method or not? Case 2: if the baseband shares the same storage unit with the main OS, then it could be easier, but where to locate the firmware, what does the firmware extension look like, converting binary files to relative files? Scenario 3: We can modify the stock ROM which contains baseband firmware. The stock ROM file contains baseband firmware which can be edited/modified or replaced with custom firmware, then we can upload it to the phone. There could be multiple cases. Please help me. I have experience in coding, custom Android firmware cooking, mobile rooting, extracting firmware of TVs/routers, etc. Please remember my ultimate goal is to transmit and receive wireless custom data using a built-in Android baseband radio chip.