First, there was a screening with the director, followed by a four-hour interview with some amateur engineers who had no knowledge of what a technical interview entails. They had just returned from school and thought they could quiz a person with 20 years of experience using university exam questions.

This was one of the worst interview processes I have ever experienced in my 20 years of work. It's as if they don't understand the interview process. First, you need to ask about what's on the CV before jumping to university-level questions.

Matrix inversion complexity? PF scheduler, etc.

Most of the questions have no relevance to the job you posted. I suggest skipping this company, as it is not worth it for wireless professionals.