Math for “Electrical Engineering & Communication Technology” recommendation

I'll assume that you know first year undergraduate level calculus. My recommendations for higher level math topics are:

1) Probability and random processes - Learn as much probability theory as you can. This is a very important prerequisite for doing any kind of work in communications. All problems in communications are modeled using random variables and random processes. You will definitely use these math concepts in your work.

2) Linear algebra - All engineers regardless of major should learn some linear algebra. In fact, it is worth it to try and learn the subject in depth. The kind of insights you get by studying it as well as the tools and techniques you learn are very useful when studying linear systems (which you encounter often in engineering).

3) Some basic complex analysis - I'm being a little imprecise here, but you should be comfortable with Laplace and Fourier transforms at the very least.

4) Real analysis - To be honest, this isn't absolutely necessary because concepts from real analysis are seldom directly applied in an engineering situation, but a course in real analysis is useful because it will teach you to think rigorously (to think a bit like a mathematician if you will).

Additionally, topics like basic graph theory and discrete math are useful if you plan to study topics like networking. Some Group theory is necessary if you plan to study error correcting codes/coding theory.