I never worked on radio modems, but I've worked on wireline modems: the issue is not the math or the standard algorithms, it's making it interoperable with everything that's existing out there and all environment conditions while working around bugs of other implementations.

It is a ridiculous amount of work and if you're new to the business, it takes a long time just to be build the lab test suite. And you need to support not just the latest and greatest protocols but also legacy ones. The operators have their own say and test labs as well and they all have slightly different setups and requirements.

> And even CPUs (esp state of art) have to worry about radio effects, as in avoiding internally and across chipset.

Radio effect are rarely an issue with regular chips. Crosstalk within a chip only happens between wires that are within hundreds of nanometers separated from each other.